SAT Math Multiple Choice Question 364: Answer and Explanation
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
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