AMC8 1993

AMC8 1993 · Q21

AMC8 1993 · Q21. It mainly tests Fractions, Area & perimeter.

If the length of a rectangle is increased by 20% and its width is increased by 50%, then the area is increased by

如果一个长方形的长增加20%，宽增加50%，那么面积增加了

(A) 10% 10%

(B) 30% 30%

(D) 80% 80%

(E) 100% 100%

Answer

Correct choice: (D)

正确答案：（D）

Solution

Answer (D): When a problem indicates a general result, then it must hold for any specific case. Therefore, suppose the original rectangle is 10 by 10 with area 100. The new length is 10 + 2 = 12 and the new width is 10 + 5 = 15. Hence the new area is 12 × 15 = 180 for an increase of 80%.

答案（D）：当题目给出一个一般性结论时，它必须对任何特定情况都成立。因此，设原来的矩形为 10×10，面积为 100。新长度为 10 + 2 = 12，新宽度为 10 + 5 = 15。因此新面积为 12×15 = 180，增加了 80%。

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