SAT Math Multiple Choice Question 153: Answer and Explanation

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Question: 153

3. If f is a function and f(4) = 5, which of the following CANNOT be the definition of f ?

  • A. f(x) = x + 1
  • B. f(x) = 2x - 3
  • C. f(x) = 3x - 2
  • D. f(x) = 4x - 11

Correct Answer: C

Explanation:

C Since the question states f(4) = 5, then when x = 4, the result should be 5. Plug in x = 4 into each answer choice to see which equation does NOT equal 5. Choice (A) becomes f(4) = 4 + 1 = 5. This works, so eliminate (A). Choice (B) becomes f(4) = 2(4) - 3 = 8 - 3 = 5. Eliminate (B). Choice (C) becomes f(4) = 3(4) - 2 = 12 - 2 = 10. The correct answer is (C).

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