Inference Critical Reasoning - GMAT Verbal

The correct answer to this question is "It is not possible for any top computer hacker to gain access to a computer equipped with the recognition software solely by virtue of skill in replicating the structure of fingerprints.". This is an INFERENCE question, requiring the test taker to choose the correct answer that must be true based on the information provided in the stimulus. "Use of the recognition software is largely impractical due to the time it takes to record and analyze a fingerprint." is incorrect as the passage provides no information with regard to the speed of recording and analyzing the fingerprint; as such, no related conclusion can be drawn. "Computers equipped with the recognition software will soon be installed in most financial firms that deal with sensitive electronic information." is incorrect as the passage provides no information with regard to the installation of computers that possess the software in specific locations; as such, no related conclusion can be drawn. "It is not possible for any top computer hacker to gain access to a computer equipped with the recognition software solely by virtue of skill in replicating the structure of fingerprints." This is the correct answer. The passage states that the software detects more characteristics than those that the most successful hackers are able to duplicate; as such, we can conclude it would be impossible for any top hacker to gain access to a protected computer solely by replicating one of multiple characteristics analyzed by the software. "Fingerprint recognition software has taken many years and tremendous investment to develop and perfect." is incorrect as the passage provides no information with regard to the time and investment costs associated with the development of the software; as such, no related conclusion can be drawn. "The fingerprint recognition software is so sensitive that many authorized users are often denied legitimate access." is incorrect as the passage provides no information with regard to errors produced by the software; as such, no related conclusion can be drawn.

Because this is an Inference question, the degree of proof for the correct answer is that the correct answer MUST BE TRUE. Because of that:

Choice "Unless the minimum wage increases, MacDowell’s will continue to remain profitable." is incorrect because you're not told what happens if the minimum wage does not increase. This prediction is hard to make, then: suppose the minimum wage stayed flat but a disease was traced to MacDowell's ingredients or a fire burned down its top-grossing store. There are plenty of ways for profitability to be cut even if the minimum wage stays flat.

Choice "If the minimum wage increases, MacDowell’s will no longer be able to remain profitable." is incorrect because it goes too far. You know that profitability will decrease, but not that it will go away entirely.

Choice "MacDowell’s will see its profitability increase if the minimum wage does not increase." is incorrect for similar reasons to choice "Unless the minimum wage increases, MacDowell’s will continue to remain profitable.". There are plenty of factors aside from the minimum wage that could decrease profitability, so choice "MacDowell’s will see its profitability increase if the minimum wage does not increase." is not necessarily true.

Choice "MacDowell’s will be unable to maintain its current profitability if the minimum wage increases." is correct. Because you're told in the argument that, of the two options that would face MacDowell's in the event of a minimum wage increase, both will decrease profitability, you know it to be true that a wage increase will cut profitability.

Choice "If MacDowell’s sees a reduction in its profitability, that means that the minimum wage has increased." is incorrect for similar reasons to "Unless the minimum wage increases, MacDowell’s will continue to remain profitable." and "MacDowell’s will see its profitability increase if the minimum wage does not increase.". Plenty of other factors can lead to a decrease in profitability, so that decrease on its own does not allow you to infer that it was specific to a minimum wage hike.

This is an Inference question. In isolation, the phrase in the question stem, “most strongly supports”, could hint at either a Strengthen question or an Inference question. However, when we take the stem in its entirety, the structure of the problem begins to unfold. Remember: premises always support conclusions. Thus, if the information in the answer choices supports the argument above, the answer choices must be premises and the conclusion is found in the argument (leading us to believe the problem is a Strengthen question.) On the other hand, if the information in the body of the question supports the answer choices below, the argument’s conclusion must be found in the answer choices (leading us to believe the problem is an Inference question.) Since the question stem indicates that the information “above” is supporting answer choices below, the answer choices must be potential conclusions. This must be an Inference question.

Two primary insights can be gleaned reading the body of the question. First, since we are looking at an Inference question, our first line of defense is the “no new information” filter. Remember that valid conclusions must always (not just sometimes) be true, and therefore must be based entirely on the information found in the premises. Conclusions containing new information not found anywhere in the argument may or may not be true. The second insight is closely linked to the first. Throughout the entire body of the question, a lot of fuzzy, non-specific words are used: “most pain relievers”, “some people”, and “many people.” They describe subgroups of the total, and are very nebulous, especially when you contrast such phrases with “all pain relievers” or “all people.” Therefore, valid conclusions that go beyond these vague categorizations may or may not be true. Believing you can conclude something about “all people” when you only know about “some people” is a logical error known as overgeneralization. Once we recognize this trick of the Testmaker, it becomes relatively easy to spot many of the wrong answer choices.

Answer choice “A physician should not advise any patient to take any pain reliever for a period of longer than 7 consecutive days.” is a classic example of overgeneralization. Notice how this conclusion focuses on “any patient” taking “any pain reliever.” The body of the question only tells us about “most people” and “most pain relievers”. This conclusion goes beyond what we know, and therefore is not necessarily true.

Answer choice “People who are sensitive to one type of pain reliever should not attempt to use a different pain reliever.” includes new information not contained in the body of the question. The evidence in the top part of the question contains nothing about people being “sensitive” to one type of pain reliever. Therefore, we cannot make a conclusion about something we don’t have information on. Answer choice “People who are sensitive to one type of pain reliever should not attempt to use a different pain reliever.” is not necessarily true.

Answer choice “At least some people who take pain relievers for longer than 7 days will experience side effects. contains no new information, and remains within the fuzzy scope of the original statements. The body of the question tells us that “many people” who take painkillers for longer than 7 days experience side effects. The conclusion that “at least some people” will experience side effects is well within the information given. “At least some people who take pain relievers for longer than 7 days will experience side effects.” is basically a restate of information already given, so we can clearly conclude it must be true. “At least some people who take pain relievers for longer than 7 days will experience side effects.” is the right answer.

The conclusion in answer choice “Any side effects experienced by a patient who has taken a pain reliever for fewer than 7 consecutive days cannot be the result of the pain reliever.” also uses extreme scope limiters not justified by the original evidence. It refers to “any side effects” that “cannot” be the result of pain relievers. This goes well beyond the scope. The problem only tells us about side effects caused by a subset of pain relievers. It makes no mention of side effects not caused by pain relievers. Answer choice “Any side effects experienced by a patient who has taken a pain reliever for fewer than 7 consecutive days cannot be the result of the pain reliever.” fails the “no new information” filter. We cannot make a conclusion about something we don’t have information on. Answer choice “Any side effects experienced by a patient who has taken a pain reliever for fewer than 7 consecutive days cannot be the result of the pain reliever.” is not necessarily true.

Answer choice “Anyone who wants to maximize their natural health and well-being should avoid pain relievers entirely.” contains all sorts of new information not contained in the original evidence. The body of the question makes no mention on how to “maximize your natural health and well-being”, nor does it give us any criteria for when we should avoid pain relievers. (For example, could it be possible that the advantages of taking pain relievers could outweigh the side effects, even if we had to deal with these negative consequences?) “Anyone who wants to maximize their natural health and well-being should avoid pain relievers entirely.” cannot be a valid conclusion.

Whenever a GMAT question asks for something that can be "properly inferred" from a critical reasoning argument, remember that your job is to fully understand the argument presented and then look for the answer choice that is guaranteed by the information presented. Remember, the information doesn't have to be interesting - it just needs to be something that must be true given the information presented.

In this case, you are told there's no correlation between the percentage of an individual's income spent on healthcare and the quality of healthcare they receive. (Further, if it did exist, the argument states that either individuals who spend a greater percentage of their income on health insurance would get better or worse quality of care.)

The only real information that you have here is the fact that increased (or decreased) spending on health insurance as a percentage of income does not "necessarily indicate quality of care." You don't have any information on absolute amounts spent on health insurance or about the health insurance itself. From this, you can eliminate "If individuals receiving free or reduced cost health insurance from the government were removed from the sample, there would be a strong correlation between cost and quality of care.", which deals with eliminating a particular type of health insurance from the sample and "Looking at the dollar amount spent on health insurance rather than the percentage would show a correlation between amount of money spent and quality of care.", which deals with absolute dollar amounts. Choice "It is probable that individuals who spend more on health insurance in fact get a lower quality of care than do those who spend less on health care." can also be eliminated since you are told that there is no correlation in either direction.

Between "Individuals who spend the greatest percentage of their income on health insurance never receive high quality of care from medical providers." and "Reducing an individual’s spending on health insurance as a percent of their income will not necessarily lead to lower quality of care.", choice "Individuals who spend the greatest percentage of their income on health insurance never receive high quality of care from medical providers." can be eliminated since there is just no way to prove that individuals who spend a large percentage of their income on health insurance never get quality care from medical providers - the entire point of the argument is that there is no correlation.

Choice "Reducing an individual’s spending on health insurance as a percent of their income will not necessarily lead to lower quality of care." must be correct. If there is no correlation between spending on health insurance as a percentage of income, then reducing spending on health insurance as a percent of income may or may not affect quality of care. The words here "will not necessarily lead to lower quality of care" are particularly important, since it links back to the argument that there is just no way to tell.

This is an inference question. The correct answer must be true. From the stimulus we know that the jury is not supposed to consider the fact that a defendant does not testify as evidence of guilt or innocence. And yet, jurors do take the refusal to testify as evidence of guilt. This means that choice "The fact that a defendant refuses to testify is sometimes unfairly considered by a jury as evidence of guilt." must be true, the fact that a defendant refuses to testify is unfairly seen by some jurors as evidence of guilt.

Choice "Most defendants who refuse to testify in their trials are, in fact, guilty." could be false, there is no indication of whether those who refuse to testify are guilty. Choice "The rules should be modified to require defendants to testify regardless of their guilt or innocence." indicates what “should” happen. This is a recommendation and is not something that must be true, even if it does seem logical. Choice "A defendant would sometimes be better served by testifying at trial rather than by choosing not to testify." could be true, a defendant might be better served by testifying, but it could be false as well. This is a prediction and it is very difficult for a prediction to be must be true. Choice "Some jurors refuse to take a defendant’s refusal to testify into consideration when deciding guilt or innocence." seems very plausible. Jurors are not supposed to take a defendant’s not testifying into account. It is logical to think that at least some jurors would follow this rule. However, it is not clear that this is the case. This does not reach the standard of must be true. The stimulus still allows the possibility that every juror takes the fact of not testifying into account.

This inference question makes you choose between a guaranteed (and almost boring) answer choice and answer choices that tend to over-generalize from the information given in the prompt. As with any inference question, it is important to pay careful attention to word play within the answers. In this case, it forces you to differentiate between two groups: ‘Top 50’ business schools in general and the subset of ‘Top 50’ business schools discussed in the prompt.

For answer choice "Accepting over 30 percent of applicants can help a business school move into the 'Top 50'.", raising the acceptance rate has nothing to do with the quality of the school or its applicants. The argument doesn’t give any information about what it takes to become a top 50 School – eliminate "Accepting over 30 percent of applicants can help a business school move into the 'Top 50'.".

Although "Most students whose GMAT scores are below 650 tend to have undergraduate grade point averages under 3.4." is tempting, the argument does not make a connection between all students whose GMAT scores are below 650 and who have grade point averages under 3.4. While this connection might be true for the students admitted to the schools discussed, the argument doesn’t address GMAT takers in general, so this inference is not guaranteed.

Similarly, answer choice "'Top 50' business schools tend to accept students with undergraduate grade point averages under 3.4." over generalizes and tries to extrapolate general tendencies among all ‘Top 50’ business schools from the information given about one fourth of that group. Because there is no indication that you can extrapolate from the information given, "'Top 50' business schools tend to accept students with undergraduate grade point averages under 3.4." is not a proper inference.

Answer choice "Work experience is not the most important criterion for admission to a 'Top 50' business school." also makes the mistake of over-generalization. While some ‘Top 50’ schools admit students without much work experience, that does not mean that work experience isn’t the most important criterion for any ‘Top 50’ business school, as suggested in "Work experience is not the most important criterion for admission to a 'Top 50' business school.'.

Answer choice "It is possible for a business school whose accepted students have average GMAT scores under 650 to be 'Top 50'." is almost guaranteed by the argument. If admitted students at 25% of the ‘Top 50’ business schools tend to have scores around 650, it is possible that the average for those schools will be around 650. Since "It is possible for a business school whose accepted students have average GMAT scores under 650 to be 'Top 50'." only requires that it be possible, it is a proper inference and is the correct answer.

The argument states that there are two unintended results of spraying chemicals in the home. Chemicals kill spiders, which would normally kill other insects found in the home. Second, insects become resistant to the chemicals over the course of generations. The correct answer will solve (or at least mitigate) one of these two problems, thus increasing the effectiveness of the chemical sprays (the goal of the question). Remember that for any inference question that inferences must be guaranteed. This may mean that they are not interesting and may add information that seems almost identical to what is given in the argument.

Remember that it’s often to find what is wrong with an answer choice than finding what works about it. Answer choice "Using only sprays that are more chemically stable" doesn’t address anything to do with the spiders or insects becoming resistant, so it can be eliminated. Alternating the chemical spray used "Alternating the use of a variety of chemical sprays used" does address the insects becoming resistant. This will improve the effectiveness of the chemical sprays, so "Alternating the use of a variety of chemical sprays used" is the correct answer.

For completion, make sure that "Increasing the amount that is sprayed", "Spraying only a portion of the house at a time", and "Planting trees outside of the house to attract certain insects that typically are resistant to chemical sprays" can be eliminated. "Increasing the amount that is sprayed" can be eliminated because increasing the amount sprayed doesn’t address the problem of resistance and may make more spiders die. "Spraying only a portion of the house at a time" can be eliminated since, while spraying one portion of the house at a time might seem like it might address the issue of resistance, it doesn’t. Planting trees that house resistant insects "Planting trees outside of the house to attract certain insects that typically are resistant to chemical sprays" would be counterproductive.

This Inference problem forces you to deal with the provided statistics, which guarantee that choice B must be true. To prove that, you could use a variable for the number of refrigerators that Fretter sold to residents of Oakland County (let's call it x) or you can borrow a tool from your Word Problems / Quantitative toolkit and pick a number (such as 50) .

You know that most (so > 1/2) of the refrigerators that Fretter sold were to residents of Oakland County. So the number of refrigerators that Fretter sold in total must be less than 2x, or less than 100.

You also know that more than 1/2 of the refrigerators sold to residents of Oakland County were NOT from Fretter. So Fretter's x (or 50) refrigerators are less than half of Oakland County's refrigerator sales. Oakland County's sales then are > 2x, or > 100. This allows you to directly compare the two totals: The number of total Fretter sales is less than the number of total Oakland County sales. Choice "In 2015, more refrigerators were purchased by residents of Oakland County than were sold by Fretter Appliances." is therefore proven.

Among the incorrect answer choices:

With choice "At least one store in Oakland County sold more refrigerators in 2015 than Fretter Appliances did.", recognize that no one store had to sell more in Oakland County than Fretter in order for Fretter's sales to be less than 50% of the county's. Several smaller stores could add up to that >50% amount.

With choice "Residents of Oakland County purchased more refrigerators in 2015 than in any previous year.", there is just no information to draw this conclusion: Fretter's 2015 was its greatest ever, but you don't have any information about Oakland County's historical sales.

Choice "Fretter Appliances sold more refrigerators to residents of Oakland County in 2015 than it did in any previous year." can be eliminated by considering extreme cases when picking numbers. If this year Fretter sold 100 refrigerators overall (its best year ever) and 51 in Oakland County (more than half its total sales), you could still have Fretter selling 90 last year (consistent with 2015 as its highest ever sales) with all 90 of them coming from Oakland County (just a much higher percentage of its sales coming from Oakland County in a previous year).

And choice "At least some residents of Oakland County purchased refrigerators from stores not located within Oakland County in 2015." is a choice that seems likely to be true, but that has no proof anywhere in the stimulus. On Inference questions, if you can't find direct proof, the answer choice is not necessarily true and must be eliminated.

This question stem is asking you to form a conclusion based on the information given, so you must pick the one answer that is guaranteed. As is true for all inference style questions, you should use process of elimination by evaluating each potential conclusion.

For "Most people eating vitamin-fortified foods are consuming dangerous amounts of vitamin C.", you do know that “most consumers overestimate the amount of one serving for these foods, ingesting two to four times what is considered one serving by the manufacturer” so it is safe to say that most people get more than their daily intake as recommended by the NAS. However, to be dangerous the recommended amounts must be “greatly exceeded” and we have no idea if “two to four times” meets that threshold. As a result this is not a proper inference.

For "Manufacturers need to change the amount listed as one serving on the packaging for vitamin-fortified foods.", there is no proof given in the stimulus that manufacturers need to do anything. While it is true that many consumers overestimate the amount of one serving, this does not allow you to conclude that manufacturers need to make a change (maybe the consumers just need to get better at estimating!). This type of prescription is virtually impossible to prove in an inference style question.

For "Any person eating vitamin-fortified foods will receive the daily intake for vitamin C that is recommended by the National Academy of Sciences.", the word “any” makes this easy to eliminate. We know that many, but not necessarily all, vitamin fortified foods contain 100% of the recommended vitamin C and that “most” consumers overestimate a serving. However, this still leaves open the possibility that some people are eating vitamin-fortified foods that do not contain vitamin C or that they are not getting a full serving’s worth.

For "Some people eating vitamin-fortified foods exceed the daily intake for vitamin C that is recommended by the National Academy of Sciences.", you know with certainty that most consumers are eating 2-4 servings of vitamin-fortified foods containing vitamin C, which provides more than 100% of the recommended amount. Since you only need to prove one person has consumed more than a serving of these foods to be sure of this conclusion, it must be true and "Some people eating vitamin-fortified foods exceed the daily intake for vitamin C that is recommended by the National Academy of Sciences." is correct.

For "People should avoid taking supplemental vitamin C if they are eating vitamin-fortified foods.", this is a similar prescription to what you saw in "Manufacturers need to change the amount listed as one serving on the packaging for vitamin-fortified foods.". There might be many reasons why someone wants or needs to take a vitamin C supplement even if they are eating the vitamin-fortified foods. Maybe their doctor wants them to have lots of extra vitamin C or maybe they are eating the vitamin-fortified foods that do not contain 100% of the recommended amount. This is not a proper inference.

With Inference questions, the correct answer has to fit the "must be true" standard, meaning that it has to be proven based on the passage; incorrect answers "could be true" but are not necessarily true based only on the information in the passage.

Here choice "The kitchen staff at Barry’s sometimes prepares multiple dishes on the same grill." fits that standard largely because of the phrase "under normal circumstances" at the end of the stimulus. If the prohibition on preparing multiple dishes on the same grill is different from "under normal circumstances," then it must be true that "sometimes" (note: "sometimes" is a very low bar to clear for proof) multiple dishes are prepared on the same grill. Choice "The kitchen staff at Barry’s sometimes prepares multiple dishes on the same grill." is therefore correct.

In contrast, notice the strong language within choice "Barry’s will not make special kitchen accommodations for diners who do not make a reservation.", that the restaurant categorically will not make kitchen accommodations (of any type) if a diner does not make a reservation. From the stimulus you know of one particular accommodation that will be made under a reservation, but you cannot conclude that there are no other possible accommodations, or that the restaurant wouldn't try to make that accommodation if someone were to arrive without a reservation.

Choice "Not all restaurants follow food allergy precautions to avoid cross-contamination between multiple dishes." could possibly be true ("not all" is another low bar of proof) but as this stimulus only tells you about one particular accommodation that one particular restaurant makes, you just do not have evidence to support this. (Note that while "not all" is a low bar, "food allergy precautions" is fairly broad: if every restaurant, for example, takes one small precaution like washing its dishes at high heat, that would be enough to rule out "Not all restaurants follow food allergy precautions to avoid cross-contamination between multiple dishes.".)

Choice "Limiting cross-contamination from multiple dishes on the same grill is the most effective way to avoid issues for diners with food allergies." is a classic example of an Inference answer choice simply going too far, using "the most effective" when you simply do not have information to rank different precautions.

And choice "Diners with food allergies are generally willing to be patient with longer wait times in order to avoid cross-contamination between dishes." is another example of a choice that might well be true, but does not have any proof in the stimulus.

This inference problem forces you to do some math to determine which answer must be true. You know from the given information that some preferences were different between the survey and the taste test (dark chocolate went from 27% to 60%, from the lowest value to the highest, so some people must have changed their preferences from either milk or white chocolate), but each answer choice will require some analysis to determine whether it "could be true" (incorrect answer) or "must be true" (correct).

Choice "The survey participants were generally inaccurate regarding their chocolate preferences." is the qualitative answer and certainly could be true, but isn't necessarily. What if this company simply has lousy white and milk chocolate, but very good dark chocolate? The respondents could have been very accurate in relaying their general preferences, but those preferences just didn't hold in this particular case. So choice "The survey participants were generally inaccurate regarding their chocolate preferences." is incorrect.

Choice "Some people who stated a preference for white chocolate in the survey preferred dark chocolate in the taste test." is more quantitative. It certainly could be true but doesn't have to be. You know that dark chocolate went from 27% to 60%, so it picked up a net gain of 33%. This could be true if some of that gain came from white and some from milk. But since you do not have the taste test totals from white and milk you can play with different combinations. Suppose all who said dark in the survey said dark in the taste test, and then 33% defected from milk to dark. That would leave white unchanged and still give you 60% dark, just with 28% white and now 12% milk. So choice B is not necessarily true and is therefore incorrect.

Choice "Some people who preferred milk chocolate in the taste test had initially stated a preference for white chocolate in the survey." does not have to be true, either. You know that 33% of respondents switched to dark chocolate, but you do not know for certain that anyone switched between white and milk. As you will see with choice "Some people who stated a preference for milk chocolate in the survey preferred dark chocolate in the taste test."...

Choice "Some people who stated a preference for milk chocolate in the survey preferred dark chocolate in the taste test." must be true. You need a net gain of 33% moving from either white or milk to dark. And since only 28% preferred white chocolate, you can't get that 33% gain unless at the very least 5% of people changed from milk to dark.

Choice "Most participants expressed a different preference in the taste test than they had indicated in the survey.​" is incorrect because, again, the minimum change is 33%. All the statements could be true if everyone who liked dark in the survey stuck with dark in the taste test, and then 33% moved to dark from milk. That case satisfies all of the facts but leaves more than half of survey responses intact, thereby invalidating choice "Most participants expressed a different preference in the taste test than they had indicated in the survey.​". Choice "Some people who stated a preference for milk chocolate in the survey preferred dark chocolate in the taste test." is correct.

As with any inference question, your job here is to understand the information given and to choose an answer choice guaranteed by the text. You are told in this stimulus to this question that free trials are meant to increase sales of the full version of an online service by giving users who would not buy the service without trying it first a chance to experiment with it. Choice "The number of people who see the free trial as an acceptable replacement for buying the online service is not greater than the number of people who buy the online service because of their experience within the free trial." is the only answer choice that is guaranteed by the text. If the number of people who find that the free trial was a good substitute is bigger than the number of people who are incentivized to buy the full online service because of the free trial, then the ability to experiment before you try the full service would not only be meaningless, it would be counter to the reason that companies offer free trials.

Among the other answers, choice "Because the cost of offering a free trial can be high, companies are often resistant to offering free trials, especially free trials that offer all features included within the paid version of the online service." can be eliminated because there is no information about what makes companies more or less likely to offer free trials. Choice "In calculating the total number of an online service sold, free trials are generally included as zero-dollar sales rather than as a separate category." can be eliminated because there is no information given about the spread of companies’ free versus paid sales. Choice "The number of sales for a given online service is directly proportional to the number of visitors to the online service's website, a number that tends to increase if a free trial is offered." can be eliminated because there is no information about whether the two values are directly proportional at all. Choice "Online services that are easily adapted to free trial versions sell better than do online services that are not readily distributed as free trials." can be eliminated for similar reasons to choice "Because the cost of offering a free trial can be high, companies are often resistant to offering free trials, especially free trials that offer all features included within the paid version of the online service.". there is no information about the importance of the ease of creating a free trial.

The answer to this Inference problem is "Last year there were more copies of accounting software sold to non-accountants than in any previous year.". Remember - in an Inference question the correct answer must be true based on the premises, and "Last year there were more copies of accounting software sold to non-accountants than in any previous year." can be proven by the facts. You know that 1) the total number of copies of accounting software was its greatest ever and that 2) the percentage that non-accountants purchased was its greatest ever (the first time over 50%). So non-accountants purchased their greatest-ever share of the greatest-ever total, meaning that they must have purchased their greatest number of copies of accounting software ever.

Among the incorrect answer choices:

"Last year more accounting software was sold to corporations than in any previous year." very well might be true, but cannot be proven. What if the growth in accounting software was entirely due to non-accountants (perhaps this was the first-ever year that a program like TurboTax was available, and so the non-accountant software surged while several accountants went out of business and didn't purchase anything)?

"At least some non-accountants purchased the most-purchased copy of software last year." also could be true, but you certainly cannot prove it. What if the most-sold software was a must-buy for any corporation but had no appeal to individuals?

"More non-accountants purchased accounting software last year than in any previous year." is close, but note the precision in language there: all the premises are about the number of copies sold, whereas "More non-accountants purchased accounting software last year than in any previous year." draws a conclusion about the number of purchasers. What if the number of purchasers stayed the same or even decreased, but each purchaser bought multiple different copies (maybe TurboTax came with a "add on Quicken for a dollar" promotion and almost everyone who purchased one piece of software last year bought two this year?).

And "Last year fewer copies of accounting software were purchased by accountants than in the previous year." of course does not have to be true as there is no proof for it anywhere. You know that the highest total number of copies of accounting software was sold so it is difficult to believe that fewer were sold to non-accountants, and that's the only real evidence you have to get close to this conclusion.

With any Inference question, you must select the answer choice that must be true based on the information in the passage. Here, several choices might seem very likely, but the "must be true" standard is crucial for inferences.

Choice "Daily meditation sessions of an hour or longer can increase one's life expectancy." must be true. The premises state that "while longer sessions produce better results, all of the above benefits (including a longer life) are possible from daily-ten minute sessions." From that, you can infer that longer sessions (an hour vs. ten minutes) would at least produce the same benefits, if not better. Additionally, note the easier-to-prove word "can" in "can increase one's life expectancy." This is much easier to prove than "will" or "only," words you see in other answer choices.

Among the other choices, choice "Mediation is only effective if it is performed on a daily basis." goes too far with "only." While the last sentence suggests that daily sessions are effective, the previous sentence uses "regular meditation" (so not necessarily "daily"), and ultimately there is nothing to suggest that even infrequent sessions are completely ineffective.

Choice "People who meditate for ten minutes each day will live longer than those who meditate less frequently." goes too far with the prediction "will" - for one, the argument doesn't give enough information to compare daily ten-minute sessions with, say, five-days-per-week hour-long sessions. But just as damning is the word "will" - predictions are just very hard to prove. Can you conceive of a situation in which people who meditate for ten minutes each day live shorter (too much radiation from their Headspace app?)? If so, "will" is not necessarily true.

Choice "It is possible to achieve as much of a gain in life expectancy from ten minutes of meditation per day as from less frequent meditation sessions of an hour or longer." is wrong for similar reasons as "Mediation is only effective if it is performed on a daily basis." is wrong: the hard fact is that "regular" meditation is more important than the duration of each session, but "regular" does not necessarily mean "daily" so this comparison is impossible to make without further information. For the same reason, choice "Meditating less frequently than once per day will lead to less positive benefits than meditating daily." is also incorrect.

This Inference problem demonstrates the importance of the "Must Be True" standard for GMAT inferences. With Inference problems, you want to attack the answer choices looking to exploit small flaws, and eliminate accordingly.

Choice "People whose diets are high in vitamin C are less likely to contract periodontitis than those whose diet are low in vitamin C." is too general and emphatic a conclusion. Even though vitamin C itself can help to prevent or treat these conditions, one cannot conclude that those who consume vitamin C will be less likely to contract those conditions. Consider a hypothetical: it could be that vitamin C alone would help, but that vitamin C is often present in sugar-containing foods and most people with high vitamin C levels are also guilty of a high sugar diet that leads to even quicker gum disease. Choice "People whose diets are high in vitamin C are less likely to contract periodontitis than those whose diet are low in vitamin C." may very well be true, but if you can create a hypothetical with a case in which it would not be true, you can eliminate it.

"Periodontitis is a condition only contracted by those who have previously contracted gingivitis." is similar: it seems like it's probably true, since you're told that gingivitis "can lead to periodontitis" but you don't know that it's the only thing that can lead to the condition (as choice "Some people suffering from periodontitis do so without having contracted gingivitis." suggests). Since you're unsure whether gingivitis is the only cause, or just one of multiple potential causes, you can eliminate both "Periodontitis is a condition only contracted by those who have previously contracted gingivitis." and "Some people suffering from periodontitis do so without having contracted gingivitis.".

Choice "A periodontitis treatment plan that does not include vitamin C is less effective than a plan that does." is also not proven. There may be other plans that do not include vitamin C but that are extremely effective. Note the language in the last sentence of the stimulus, that vitamin C "can help to treat periodontitis." "Can help" is soft language that leaves plenty of room for another treatment program to be even more helpful.

Choice "Increasing the amount of vitamin C in one’s diet has helped some periodontitis patients reduce the severity of that condition." is correct, in large part because of similarly soft language. If vitamin C can help treat the condition, that means that it must have helped at least some patients in treatment. That's an easy bar to get over, and since you know for a fact that vitamin C is helpful, you can clear that bar. Choice "Increasing the amount of vitamin C in one’s diet has helped some periodontitis patients reduce the severity of that condition." is correct.

The stimulus states that "...health insurance companies paid for a smaller percentage of claims last year than they did ten years ago." This means that the companies had a greater percentage of unpaid claims last year. Put another way, they had a smaller percentage of unpaid claims ten years ago, which is what choice "the percentage of health insurance claims that were unpaid was less than last year's percentage." says.

Choice "fewer people made health insurance claims than was the case last year." is incorrect because the number of people making claims is never mentioned. One person can make several claims, so we cannot draw any inferences about the number of people.

"more claims were not paid by insurance companies than were not paid last year." is wrong because the overall number of claims and the percentage of claims not paid were both lower ten years ago. Since they were both lower, their product (Total * Percentage) would also be lower, disproving the statement that more claims were not paid.

Answer "health insurance companies paid a greater percentage of their claims than they paid twenty years ago." is incorrect because we do not have any way of knowing the difference in the percentage of claims paid for these two periods (ten years ago versus twenty years ago).

Answer "profits made by health insurance companies were similar to profits made by health insurance companies last year." is incorrect since we already know that the companies have compensated for paying more real dollars by hiking their rates, but there are too many other factors involved in determining profit to make this comparison.

With Inference questions, the correct answer has to fit the "must be true" standard, meaning that it has to be proven based on the passage; incorrect answers "could be true" but are not necessarily true based only on the information in the passage.

Here choice "The kitchen staff at Barry’s sometimes prepares multiple dishes on the same grill." fits that standard largely because of the phrase "under normal circumstances" at the end of the stimulus. If the prohibition on preparing multiple dishes on the same grill is different from "under normal circumstances," then it must be true that "sometimes" (note: "sometimes" is a very low bar to clear for proof) multiple dishes are prepared on the same grill. Choice "The kitchen staff at Barry’s sometimes prepares multiple dishes on the same grill." is therefore correct.

In contrast, notice the strong language within choice "Barry’s will not make special kitchen accommodations for diners who do not make a reservation.", that the restaurant categorically will not make kitchen accommodations (of any type) if a diner does not make a reservation. From the stimulus you know of one particular accommodation that will be made under a reservation, but you cannot conclude that there are no other possible accommodations, or that the restaurant wouldn't try to make that accommodation if someone were to arrive without a reservation.

Choice "Not all restaurants follow food allergy precautions to avoid cross-contamination between multiple dishes." could possibly be true ("not all" is another low bar of proof) but as this stimulus only tells you about one particular accommodation that one particular restaurant makes, you just do not have evidence to support this. (Note that while "not all" is a low bar, "food allergy precautions" is fairly broad: if every restaurant, for example, takes one small precaution like washing its dishes at high heat, that would be enough to rule out "Not all restaurants follow food allergy precautions to avoid cross-contamination between multiple dishes.".)

Choice "Limiting cross-contamination from multiple dishes on the same grill is the most effective way to avoid issues for diners with food allergies." is a classic example of an Inference answer choice simply going too far, using "the most effective" when you simply do not have information to rank different precautions.

And choice "Diners with food allergies are generally willing to be patient with longer wait times in order to avoid cross-contamination between dishes." is another example of a choice that might well be true, but does not have any proof in the stimulus.

This inference problem forces you to do some math to determine which answer must be true. You know from the given information that some preferences were different between the survey and the taste test (dark chocolate went from 27% to 60%, from the lowest value to the highest, so some people must have changed their preferences from either milk or white chocolate), but each answer choice will require some analysis to determine whether it "could be true" (incorrect answer) or "must be true" (correct).

Choice "The survey participants were generally inaccurate regarding their chocolate preferences." is the qualitative answer and certainly could be true, but isn't necessarily. What if this company simply has lousy white and milk chocolate, but very good dark chocolate? The respondents could have been very accurate in relaying their general preferences, but those preferences just didn't hold in this particular case. So choice "The survey participants were generally inaccurate regarding their chocolate preferences." is incorrect.

Choice "Some people who stated a preference for white chocolate in the survey preferred dark chocolate in the taste test." is more quantitative. It certainly could be true but doesn't have to be. You know that dark chocolate went from 27% to 60%, so it picked up a net gain of 33%. This could be true if some of that gain came from white and some from milk. But since you do not have the taste test totals from white and milk you can play with different combinations. Suppose all who said dark in the survey said dark in the taste test, and then 33% defected from milk to dark. That would leave white unchanged and still give you 60% dark, just with 28% white and now 12% milk. So choice B is not necessarily true and is therefore incorrect.

Choice "Some people who preferred milk chocolate in the taste test had initially stated a preference for white chocolate in the survey." does not have to be true, either. You know that 33% of respondents switched to dark chocolate, but you do not know for certain that anyone switched between white and milk. As you will see with choice "Some people who stated a preference for milk chocolate in the survey preferred dark chocolate in the taste test."...

Choice "Some people who stated a preference for milk chocolate in the survey preferred dark chocolate in the taste test." must be true. You need a net gain of 33% moving from either white or milk to dark. And since only 28% preferred white chocolate, you can't get that 33% gain unless at the very least 5% of people changed from milk to dark.

Choice "Most participants expressed a different preference in the taste test than they had indicated in the survey.​" is incorrect because, again, the minimum change is 33%. All the statements could be true if everyone who liked dark in the survey stuck with dark in the taste test, and then 33% moved to dark from milk. That case satisfies all of the facts but leaves more than half of survey responses intact, thereby invalidating choice "Most participants expressed a different preference in the taste test than they had indicated in the survey.​". Choice "Some people who stated a preference for milk chocolate in the survey preferred dark chocolate in the taste test." is correct.

As with any inference question, your job here is to understand the information given and to choose an answer choice guaranteed by the text. You are told in this stimulus to this question that free trials are meant to increase sales of the full version of an online service by giving users who would not buy the service without trying it first a chance to experiment with it. Choice "The number of people who see the free trial as an acceptable replacement for buying the online service is not greater than the number of people who buy the online service because of their experience within the free trial." is the only answer choice that is guaranteed by the text. If the number of people who find that the free trial was a good substitute is bigger than the number of people who are incentivized to buy the full online service because of the free trial, then the ability to experiment before you try the full service would not only be meaningless, it would be counter to the reason that companies offer free trials.

Among the other answers, choice "Because the cost of offering a free trial can be high, companies are often resistant to offering free trials, especially free trials that offer all features included within the paid version of the online service." can be eliminated because there is no information about what makes companies more or less likely to offer free trials. Choice "In calculating the total number of an online service sold, free trials are generally included as zero-dollar sales rather than as a separate category." can be eliminated because there is no information given about the spread of companies’ free versus paid sales. Choice "The number of sales for a given online service is directly proportional to the number of visitors to the online service's website, a number that tends to increase if a free trial is offered." can be eliminated because there is no information about whether the two values are directly proportional at all. Choice "Online services that are easily adapted to free trial versions sell better than do online services that are not readily distributed as free trials." can be eliminated for similar reasons to choice "Because the cost of offering a free trial can be high, companies are often resistant to offering free trials, especially free trials that offer all features included within the paid version of the online service.". there is no information about the importance of the ease of creating a free trial.