每日一题

Mathematics>Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

The length of a rectangle is increased by 20%, and the width of the rectangle is increased by 30%. By what percentage will the area of the rectangle be increased?

(A) 25%
(B) 36%
(C) 50%
(D) 56%
(E) 60%

答案和解析

答案：D

解析：

Let l and W be the orlglnal length and wldth of the rectangle, respectlvely. lf we denote by L and W the new length and wldth of the rectangle, respectlvely, then we have:

L=l+(20/100)l=1.2l and
W=w+(30/100)w=1.3w
So, the new area wlll be:
A=L*W=(1.2l)*(1.3w)=1.56(l*w)
1.56(l*w)=lw+0.56(lw)

where (lw) is the orlglnal area of the rectangle.
So the area is lncreased by 56%