AMC8 2007

AMC8 2007 · Q17

AMC8 2007 · Q17. It mainly tests Fractions, Mixture / concentration.

A mixture of 30 liters of paint is 25% red tint, 30% yellow tint and 45% water. Five liters of yellow tint are added to the original mixture. What is the percent of yellow tint in the new mixture?

一种 30 升的油漆混合物含有 25% 红色颜料、30% 黄色颜料和 45% 水。在原混合物中加入 5 升黄色颜料。新混合物中黄色颜料的百分比是多少？

(A) 25 25

(B) 35 35

(D) 45 45

(E) 50 50

Answer

Correct choice: (C)

正确答案：（C）

Solution

(C) There are 0.30(30) = 9 liters of yellow tint in the original 30-liter mixture. After adding 5 liters of yellow tint, 14 of the 35 liters of the new mixture are yellow tint. The percent of yellow tint in the new mixture is $100\times\frac{14}{35}=100\times\frac{2}{5}$ or 40%.

(C) 原来 30 升的混合液中，黄色染料占 $0.30(30)=9$ 升。加入 5 升黄色染料后，新混合液共有 35 升，其中 14 升是黄色染料。新混合液中黄色染料所占百分比为 $100\times\frac{14}{35}=100\times\frac{2}{5}$，即 40%。

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