SAT Math Multiple Choice Question 364: Answer and Explanation

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Test Information

Question: 364

4. The function f(x) is defined as f(x) = 2g(x), where g(x) = x + 5. What is the value of f(3)?

  • A. -4
  • B. 6
  • C. 8
  • D. 16

Correct Answer: D

Explanation:

D

Difficulty: Easy

Category: Passport to Advanced Math / Functions

Strategic Advice: Understanding function notation will earn you valuable points on Test Day. When you see an expression such as f(x), it means to substitute the given value for x in the function's equation. When there is more than one function involved, pay careful attention to which function should be evaluated first.

Getting to the Answer: You are looking for the value of f(x) at x = 3. Because f(x) is defined in terms of g(x), evaluate g(3) first by substituting 3 for x in the expression x + 5.

g(3) = 3 + 5 = 8

f(3) = 2g(3) = 2(8) = 16

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