SAT Math Multiple Choice Question 21: Answer and Explanation

Home > SAT Test > SAT Math Multiple Choice Practice Tests

Test Information

Question: 21

1. The length of a certain rectangle is twice the width. If the area of the rectangle is 128, what is the length of the rectangle?

  • A. 4
  • B. 8
  • C. 16
  • D. 21

Correct Answer: C

Explanation:

C Plug in the answers. If you start with (B), the length is 8, and the width is half that, or 4. Area is length × width. The area of this rectangle is 8 × 4, which is nowhere near 128. Eliminate (A) and (B), as both are too small. Try (C): If the length is 16, the width is 8. So, does 128 = 16 × 8? You could write it all out, since you can't use your calculator, but you can also estimate. 16 × 10 = 160, so 16 × 8 would be about 130. The number in (D) is too large and will give a weird fraction, so (C) is correct. Alternatively, write an equation. The equation is area = w × 2w. So, 128 = 2w2. Divide by 2 to get 64 = w2. Take the square root of both sides to find w = 8. The length is twice this width, so length = 2 × 8 = 16, and the answer is (C).

Previous       Next