PSAT Math Multiple-Choice Question 239: Answer and Explanation

Question: 239

If f(x) = 3x + 5, what is f(6) - f(2) ?

• A. 11
• B. 12
• C. 17
• D. 23

Correct Answer: B

Explanation:

B

Difficulty: Medium

Category: Passport to Advanced Math/Functions

Getting to the Answer: When evaluating a function, substitute the value inside the parentheses for x in the equation. Evaluate the function at x = 6 and at x = 2, and then subtract the second output from the first. Note that this is not the same as first subtracting 6 - 2 and then evaluating the function at x = 4:

f(6) = 3(6) + 5 = 18 + 5 = 23

f(2) = 3(2) + 5 = 6 + 5 = 11

f(6) - f(2) = 23 - 11 = 12

Choice (B) is correct.