SAT Math Multiple Choice Practice Question 493: Answer and Explanation

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Question: 493

13. If x = y + 1 and y ≥ 1, then which of the following is equal to x2 - y2 ?

A. (xy)2
B. x2y – 1
C. x + y
D. x2 – 1
E. y2 + 1

Correct Answer: C

Explanation:

C Whenever there are variables in the answer choices, you should plug in. Because x = y + 1 and y ≥ 1, you can make x = 5 and y = 4. In that case, x2y2 = 25 – 16 = 9, so 9 is your target answer. When you plug x = 5 and y = 4 into the answer choices, only C gives you 9. Plugging In turns a hard question into a much easier question.

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