GRE Math : Statistics

Study concepts, example questions & explanations for GRE Math

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Example Questions

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Example Question #1 : Statistics

The medians of the following two sets of numbers are equal, and
the sets are arranged in ascending order
{1, 4, x, 8} and {2, 5, y, 9}. What is y – x?

Possible Answers:

0

2

–2

–1

3

Correct answer:

–1

Explanation:

Answer: –1
Explanation: Recall that the median of an even-numbered set of numbers is the arithmetic mean of the pair of middle terms. Thus (4 + x)/2 = median of the first set and (5 + y)/2 = median of the second set. Since both medians are equal, we can set the equations equal to eachother. (4 + x)/2 = (5 + y)/2. Multiply both sides by 2 and we get 4 + x = 5 + y. We also know that 4 < x < 8 and 5 < y < 9, since the sets are arranged in ascending order. This narrows our options for x and y down significantly. Plugging in various values will eventually get you to x = 7 and y = 6, since 7 + 4 = 11 and 5 + 6 = 11, and thus the median in both cases would be 5.5. Thus, y – x = –1.

Example Question #1 : Statistics

What is the median in the following set of numbers?

16, 19, 16, 7, 2, 20, 9, 5

Possible Answers:

Correct answer:

Explanation:

16, 19, 16, 7, 2, 20, 9, 5

Order the numbers from smallest to largest.

2,5,7,9,16,16,19,20

The median is the number in the middle.

In this case, there is a 9 and 16 in the middle.

When that happens, take the average of the two numbers.

Example Question #1 : Statistics

Find the median:

Possible Answers:

Correct answer:

Explanation:

To find the median, arrange the numbers from smallest to largest:

 4,4,4,4,6,7,9,9,12,12,12,12,12,12,18,76,90

There are 17 numbers in total.  Since 17 is an odd number, the median will be the middle number of the set.  In this case, it is the 9th number, which is 12.

Example Question #1 : How To Find Median

There are 3,500 people in group A and 5,000 people in group B:

Car Type

% in Group A Who Own

% in Group B Who Own

Motorbike

 4

 9

Sedan

 35

 25

Minivan

 22

 15

Van

 9

 12

Coupe

 3

 6

What is the median of the number of people in group B who own either a minivan, van, or coupe?

Possible Answers:

Correct answer:

Explanation:

Treat the percentages as a list, as we are including every demographic from the 3 vehicle types mentioned. If we do each 0.06(5000), 0.12(5000), and 0.15(5000) we note from observation that the median, or middle value, would have to be the 12% row since the sample size does not change. The question asks for EITHER of the 3 categories, so we can ignore the other two.

0.12(5000) = 600 (van) is the median of the 3 categories.

Example Question #1 : How To Find Median

In the set above, which is larger: the median, the mean, or the mode?

Possible Answers:

Mean

All are equal

Both median and mean

Median

Mode

Correct answer:

Mean

Explanation:

Begin by ordering the set from smallest to largest:

 

Already, we see that the mode is 8. Find the median by taking the average of the two middle numbers:

Find the mean by adding all numbers and dividing by the total number of terms:

 

Of the three, the mean of the set is the largest.

Example Question #1 : Statistics

The grades on a test taken by  students are  respectively. What was the median score for this test?

Possible Answers:

Correct answer:

Explanation:

To solve this problem, we must be aware of the definition of a median for a set of numbers. The median is defined as the number that is in middle of a set of numbers sorted from smallest to largest. Therefore we must first sort the numbers from largest to smallest.

 

34,43,45,50,56,65,70,76,76,82,87,88,92,95,100

43,45,50,56,65,70,76,76,81,87,88,82,95

45,50,56,65,70,76,76,81,87,88,82

50,56,65,70,76,76,81,87,88

56,65,70,76,76,81,87

65,70,76,76,81

70,76,76

76

Then by slowly eliminating the smallest and the largest numbers we find that the median score for this test is 76.

Example Question #2 : Statistics

Quantity A: The mean of 

Quantity B: The median of 

Possible Answers:

The relationship cannot be determined.

Quantity A is greater.

The two quantities are equal.

Quantity B is greater.

Correct answer:

Quantity B is greater.

Explanation:

Begin by reordering the set in numerical order:

Then becomes

Since there is an odd number of values, the median is the middle value.

Quantity B: 

Now, to find the arithmetic mean, take the sum of values divided by the total number of values.

Quantity A: 

Example Question #2 : Statistics

The arithmetic mean of  is 

 The median of 

Possible Answers:

Correct answer:

Explanation:

 is an unknown value, but it can be found given what we know about the mean of the set :

Now,  is out of order; arrange in numerically:

Since there are even number of values, the median is the mean of the two middle most values:

Example Question #2 : Statistics

Column A                                                  

The mean of the sample of numbers 2, 5, and 10.                           

Column B 

The mean of the sample of numbers 1, 5, and 15.

Possible Answers:

The quantity in Column B is greater.

The two quantities are equal.

The relationship cannot be determined from the information given.

The quantity in Column A is greater.

Correct answer:

The quantity in Column B is greater.

Explanation:

The arithmetic mean is the average of the sum of a set of numbers divided by the total number of numbers in the set. This is not to be confused with median or mode.

In Column A, the mean of 5.66 is obtained when the sum (17) is divided by the number of values in the set (3).

In Column B, the mean of 7 is obtained when 21 is divided by 3. Because 7 is greater than 5.66, Column B is greater. The answer is Column B.

Example Question #1 : Statistics

Bill runs for 30 minutes at 8 mph and then runs for 15 minutes at 13mph. What was his average speed during his entire run?

Possible Answers:

10 mph

101/2 mph

92/3 mph

11 mph

Correct answer:

92/3 mph

Explanation:

Rate = distance/time.

Find the distance for each individual segment of the run (4 miles and 3.25miles). Then add total distance and divide by total time to get the average rate, while making sure the units are compatible (miles per hour not miles per minute), which means the total 45 minute run time needs to be converted to 0.75 of an hour; therefore (4miles + 3.25 miles/0.75 hour) is the final answer.

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