AMC8 2009
AMC8 2009 · Q8
AMC8 2009 · Q8. It mainly tests Fractions, Arithmetic misc.
The length of a rectangle is increased by 10% and the width is decreased by 10%. What percent of the old area is the new area?
矩形的长度增加10%，宽度减少10%。新面积是原面积的百分之多少？
(A)
90
90
(B)
99
99
(C)
100
100
(D)
101
101
(E)
110
110
Answer
Correct choice: (B)
正确答案：（B）
Solution
Answer (B): A rectangle with length $L$ and width $W$ has area $LW$. The new rectangle has area $(1.1)L \times (0.9)W = 0.99LW$. The new area $0.99LW$ is $99\%$ of the old area.
答案（B）：一个长为 $L$、宽为 $W$ 的长方形面积为 $LW$。新的长方形面积为 $(1.1)L \times (0.9)W = 0.99LW$。新的面积 $0.99LW$ 是原来面积的 $99\%$。
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