1953 AMC 12 第 9 题

Question

要把

9

盎司、酒精含量为

50\%

的剃须水稀释成酒精含量为

30\%

的剃须水，需要加入的水为：

The number of ounces of water needed to reduce

9

ounces of shaving lotion containing

50\%

alcohol to a lotion containing

30\%

alcohol is:

3

4

5

6

7

加水时，酒精的量保持不变

The amount of alcohol stays fixed when water is added

根据加水量列出

\frac{4.5}{9+w}=0.30

Set

\frac{4.5}{9+w}=0.30

剃须水中原有

9(0.50)=4.5

盎司酒精。若加入

w

盎司水，则

\frac{4.5}{9+w}=0.30\text{。}

所以

9+w=15

，且

w=6

。

因此，正确答案是 D。

The lotion initially contains

9(0.50)=4.5

ounces of alcohol. If

w

ounces of water are added, then

\frac{4.5}{9+w}=0.30.

Hence

9+w=15

and

w=6.

Thus, the correct answer is D.

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