SAT Math Multiple Choice Practice Question 473: Answer and Explanation

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Question: 473

14. Question below refers to the following definition.

For all real numbers x, let f(x) = 2x2 + 4.

Which of the following is equal to f(3) + f(5)?

A. f(4)
B. f(6)
C. f(8)
D. f(10)
E. f(15)

Correct Answer: B


B To find the value of f(3) + f(5), find the values of f(3) and f(5) separately: f(3) = 2(3)2 + 4 = 22 and f(5) = 2(5)2 + 4 = 54. So f(3) + f(5) = 76. You already know that f(4) = 36 from question 12, so you can cross out A. C is the Joe Bloggs answer because Joe simply adds 3 and 5, and it can't be that easy. If you ballpark D and E, putting 10 or 15 in the function will give you a number bigger than 100, and you're looking for 76, so D and E are too big. That means the answer is B by POE.

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