SAT Math Multiple Choice Practice Question 11: Answer and Explanation

Next steps

Question: 11

11. Let &x be defined as x + 3 if x is prime, and as 2x if x is composite. Which of the following would produce a result of 18?

I. &15

II. &9

III. &36

A. I only
B. II only
C. III only
D. both I and II
E. both II and III

Correct Answer: B

Explanation:

B. Because 15 is composite (it's 3 × 5), &15 = 2(15) = 30. 9 is also composite, so &9 = 2(9) = 18. 36 is composite, too, and &36 = 2(36) = 72. Only option II works, so Choice (B) is the correct answer.

A prime number is divisible only by itself and 1. A composite number is anything that isn't prime or special. (Zero and one are considered "special" numbers.) Turn to Chapter 12 for more information on these types of numbers.

Previous       Next