SAT Math Multiple Choice Practice Question 76: Answer and Explanation
10. What is the length of a rectangle whose perimeter is 40 inches and whose width is 8 inches?
A. 21/2 inches
B. 5 inches
C. 12 inches
D. 16 inches
E. 32 inches
Correct Answer: C
C. As always, using a drawing to help you visualize a problem can't hurt:
Notice that I put 8 inches on two sides. Don't write something like x + 8 = 40; a rectangle has four sides, not two. If you call the two missing sides in the diagram x, the equation is x + x + 8 + 8 = 40, or 2x + 16 = 40. Then 2x = 24, and x = 12.