AMC10 2012 A

AMC10 2012 A · Q7

AMC10 2012 A · Q7. It mainly tests Ratios & proportions.

In a bag of marbles, $\frac{3}{5}$ of the marbles are blue and the rest are red. If the number of red marbles is doubled and the number of blue marbles stays the same, what fraction of the marbles will be red?

一袋弹珠中，$\frac{3}{5}$是蓝色的，其余是红色的。如果红色的弹珠数量加倍，蓝色的数量不变，那么红色的弹珠占总数的几分之几？

(A) \frac{2}{5} \frac{2}{5}

(B) \frac{3}{7} \frac{3}{7}

(D) \frac{3}{5} \frac{3}{5}

(E) \frac{4}{5} \frac{4}{5}

Answer

Correct choice: (C)

正确答案：（C）

Solution

The ratio of blue marbles to red marbles is 3 : 2. If the number of red marbles is doubled, the ratio will be 3 : 4, and the fraction of marbles that are red will be $\frac{4}{3+4} = \frac{4}{7}$.

蓝色的弹珠与红色的弹珠的比例是3 : 2。如果红色的弹珠数量加倍，则比例变为3 : 4，红色的分数为$\frac{4}{3+4} = \frac{4}{7}$。

Topics

AR.004 Ratios & proportions