SAT Math Multiple Choice Practice Question 32: Answer and Explanation

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Question: 32

10. Set S contains the numbers 20 to 40, inclusive. If a number is chosen at random from S, what is the probability that this number is even?

A. 10/20
B. 11/20
C. 10/21
D. 11/21
E. 12/21

Correct Answer: D


D. First off, you must realize that the set contains 21 numbers, not 20. Remember that to find the size of a list of numbers, you subtract the first and last numbers and then add one. (Count them if you don't believe me.) Now, the even numbers are 20, 22, . . . up to 40, which makes five numbers in the 20s, five in the 30s, and 40, which makes 11 numbers out of 21.

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