SAT Math Multiple Choice Question 48: Answer and Explanation

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Question: 48

4. If f(x) = 2x2 + 4 for all real numbers x, which of the following is equal to f(3) + f(5) ?

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

Correct Answer: B

Explanation:

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 can tell that f(4) will be between 22 and 54, so you can cross out (A). If you ballpark (C) and (D), putting 10 or 15 in the function will give you a number bigger than 100, and you're looking for 76, so (C) and (D) are too big. That means the answer is (B) by POE.

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