SAT Math : How to find the probability of an outcome

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #131 : How To Find The Probability Of An Outcome

Forty balls are placed in a large box, each marked with a whole number from 1 to 40. The balls marked with an even number or a prime number are all blue; the other balls are red.

Two balls are drawn without replacement. Give the probability that both will be red.

Possible Answers:

Correct answer:

Explanation:

The odd composite numbers  - that is, the odd numbers that have more than two factors - are all represented by red balls. The odd composite whole numbers in the set  comprise the set  - a set of eight elements. The ball marked "1" is also red, since 1 is odd and neither composite nor prime. Therefore, 9 balls of the 40 are red.

We can assume that the two balls are drawn one at a time. The probability of the first ball being red is . Since there are now 39 balls, 8 of which are red, the probability that the second ball will be red is . The probabilities are multiplied:

.

This is the probability that both balls will be red.

Example Question #132 : How To Find The Probability Of An Outcome

Scrabble

A popular word game has 100 square tiles. Each is marked with a letter or a blank; the distribution of the letters is seen in the table above. Note that two of the tiles are blanks.

Two letters are drawn at random from the set of tiles. What is the probability that both tiles will be marked with a letter from the first half of the alphabet?

Possible Answers:

None of the other choices gives the correct response.

Correct answer:

Explanation:

Add the numbers of tiles corresponding to each of the letters from "A" to "M":

Scrabble 2

The probability that one of these tiles will be drawn on the first draw is . On the second draw, there will be 52 such tiles out of 99, making the probability of the same event . The probability of both draws resulting in one of these letters is the product of these individual probabilities:

Example Question #133 : How To Find The Probability Of An Outcome

Scrabble

A popular word game has 100 square tiles. Each is marked with a letter or a blank; the distribution of the letters is seen in the table above. Note that two of the tiles are blanks.

Two letters are drawn at random without replacementfrom the set of tiles. What is the probability that neither tile is marked with a consonant?

(Note: "Y" is considered a consonant for purposes of this problem.)

Possible Answers:

Correct answer:

Explanation:

Out of the 100 tiles, there are 9 tiles marked with "A", 12 with "E", 9 with "I", 8 with "O", and 4 with "U", as well as 2 blank tiles; this is a total of

tiles not marked with a consonant.

The probability that the first draw will result in a vowel or a blank is .

After this draw, there will be 99 tiles, 43 of which are vowels or blanks; the probability that the second draw will be one of these is .

Use the multiplication principle to find the probability that both tiles will be vowels or blanks:

Example Question #134 : How To Find The Probability Of An Outcome

A six-sided die is rolled twice. What is the probability that the first roll will land on an odd number, and the second roll will land on a even number? 

Possible Answers:

Correct answer:

Explanation:

A six-sided die has three sides with odd numbers and three sides with even numbers. Thus, the probability of the die landing on an odd number is 

which simplifies to 

.

The probability of the die landing on an even number is also 

which we can simplify to 

Because the probabilities are independent of each other, we can find the probability of the two events happening in a row by multiplying the fractions. 

Therefore, the probability of the first roll landing on an odd number, and the second roll landing on an even number is  .

 

Example Question #135 : How To Find The Probability Of An Outcome

You went to order a cake but all of the cakes are in identical boxes. If there are five chocolate cakes, four carrot cakes, three vanilla cakes, and six red velvet cakes, what is the maximum number of boxes that you would have to open to ensure that you have one of each type of cake?

Possible Answers:

16

9

12

4

Correct answer:

16

Explanation:

There are four different types of cake. In this type of problem we want to guarantee we have one of each, so we need to assumbe we have very bad luck. We start with the red velvet since that is the type with the most cakes. If we open those 6 we are not guaranteed to have different ones. Then say we opened all five chocolate cakes, then all four carrot cakes. We still have only three types of cakes but opened 15 boxes. When we open the next box (16) we will be guaranteed to have one of each.

 

 

 

Example Question #136 : How To Find The Probability Of An Outcome

What is the probability of drawing either an ace, a king, or a jack from a standard deck of playing cards?

Possible Answers:

Correct answer:

Explanation:

Remember that the "probability" of an event happening is the number of outcomes which result in that event divided by the total number of possible outcomes. That is,

.

Hence, the probability of an event happening is described as a fraction. To solve this problem, we must first recognize that three separate events are being described: drawing an ace, drawing a king, and drawing a jack. Because each of these events do not overlap (you cannot, for example, draw a card that is both a jack and a king at the same time), calculating the probability  that you draw any one of them is a simple matter of adding together their respective probabilities , and .

There are  cards in a deck of playing cards,  of which are aces,  of which are kings, and  of which are jacks. Hence, 

, and

,

and therefore

This means that the probability of drawing either an ace, a king, or a jack from a standard deck of playing cards is .

Example Question #12 : New Sat Math Calculator

Mrs. Smith assigns homework to her class once a week and records each student's results. For last week's assignment, the histogram depicts these results. If the homework set was worth twenty points, what is the range of grades for last week's assignment?

Note: For each error, one point is subtracted from the total points possible. 

Screen shot 2016 02 10 at 10.32.20 am

Possible Answers:

Correct answer:

Explanation:

Mrs. Smith assigns homework to her class once a week and records each student's results. For last week's assignment, the histogram depicts these results. If the homework set was worth twenty points, what is the range of grades for last week's assignment?

Note: For each error, one point is subtracted from the total points possible. 

To solve this problem, first identify what the highest and lowest grade on the assignment was. The highest grade will be the one with the least amount of errors made and the lowest grade will be the one with the most amount of errors made.

The red bar in the histogram says that students made between zero and two errors. In other words, either: 0, 1, 2 errors.

The yellow bar in the histogram says that the students made between two and four errors. Since the red bar includes two errors the yellow bar only includes 3 or 4 errors.

The green bar in the histogram says that students made 5 or 6 errors.

The teal bar in the histogram says that students made 7 or 8 errors.

The blue bar in the histogram says that students made 9 or 10 errors.

The purple bar in the histogram says that students made 11 or 12 errors.

Screen shot 2016 02 10 at 10.32.20 am

This means that at least one student made zero errors on the assignment and therefore did not loose any points. Therefore, the highest grade on the assignment was twenty.

The histogram shows that at least one student made twelve errors on the test. Therefore, the lowest grade on the assignment would be:

From here, calculate the range.

Example Question #9 : How To Find The Answer From A Table

Use the following table to answer the question.

Table2

How many students received an A in math?

Possible Answers:

Correct answer:

Explanation:

When looking at the table

Table2

we can see that is shows several students and within the subjects of Math, Science, and Art what grades those students received in those classes.

So, going over the table briefly, we can see the first student Katrina.  We see for Math she received an A.  For science, Katrina received an A.  And for Art, Katrina got a B.  We can read the table similarly for the remaining students.

Now, the question asks how many students received an A in math.  So we will look through the table and locate Math.  Once we locate Math, we will look at the grade that corresponds with it (In this example, we do not care about who the student is.  We just care about the grade).  So, we will count the number of A's we see matched up to the subject Math.

Once we do that, we see there are 3 students who received A's in Math (Katrina, Chris, and Fionn).

Example Question #138 : How To Find The Probability Of An Outcome

Use the following table to answer the question.

Table2

What class did Craig have the highest grade in?

Possible Answers:

Correct answer:

Explanation:

Let's look at the table.

Table2

We can see the first column lists all the students.  The next column shows all of the classes.  And the last column shows the grade they received in those classes.


Now, to find which class Craig received the highest grade, we must first locate Craig.  We can see all of Craig's classes are at the very bottom of the table.

Now, we will look at the grade he got in each class by following along the rows with Craig's name.

 

We can see Craig's first class is Math.  He received a B.

Craig's second class is Science.  He received an A.

Craig's third class is Art.  He received a B.

 

Knowing this, we can see the highest grade Craig received was an A.  The class where he received an A was Science.

Therefore, the class that Craig received the highest grade was Science.

Example Question #139 : How To Find The Probability Of An Outcome

Use the following table to answer the question:

Table2

What grade did Chris receive in Science?

Possible Answers:

Correct answer:

Explanation:

To answer the question, let's look at the table.

Table2

We can see the first column shows the different students, the next column shows the classes they are in, and the last column shows their grade in the class.

Now, to find what grade Chris received in Science, we will first locate Chris' name in the first column.

Now, we can see his name appears 3 times.  If we look to the right, we can see his name matches up to 3 different classes:  Math, Science, and Art.  We want to know his grade in Science, so we will choose that row.  

We will again look to the right to see the grade.  We can see that it says A.

Therefore, the grade that Chris received in Science was an A.

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