SAT Math Multiple Choice Question 24: Answer and Explanation
4. If y = 3x and x and y are both integers, which of the following is equivalent to 9x + 3x + 1 ?
- A. y3
- B. 3y + 3
- C. y(y + 3)
- D. y2 + 3
Correct Answer: C
C We've got variables in the answer choices, which means this is a perfect Plug In problem. Since we can't use calculators, let's make up an easy value for x, such as 2. 9x + 3x+1 then becomes 92 + 32+1 = 81 + 27 = 108. We plugged in x = 2, so let's use that to find y: y = 3x, so y = 32 = 9. Now plug in y = 9 to each answer choice to see which one gives you 108. Choice (C) is y(y + 3), which is 9(12) = 108, which is the correct answer.