AMC12 2018 A

AMC12 2018 A · Q1

AMC12 2018 A · Q1. It mainly tests Percent, Arithmetic misc.

A large urn contains 100 balls, of which 36% are red and the rest are blue. How many of the blue balls must be removed so that the percentage of red balls in the urn will be 72%? (No red balls are to be removed.)

一个大瓮中有100个球，其中36%是红色的，其余是蓝色的。需要移除多少个蓝球，使得瓮中红球的百分比变为72%？（不得移除红球。）

(A) 28 28

(B) 32 32

(D) 50 50

(E) 64 64

Answer

Correct choice: (D)

正确答案：（D）

Solution

There are currently 36 red balls in the urn. In order for the 36 red balls to represent 72% of the balls in the urn after some blue balls are removed, there must be $36 \div 0.72 = 50$ balls left in the urn. This requires that $100 - 50 = 50$ blue balls be removed.

瓮中目前有36个红球。为了使36个红球在移除一些蓝球后占瓮中球的72%，瓮中剩余球数必须为$36 \div 0.72 = 50$。因此需要移除$100 - 50 = 50$个蓝球。

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