AMC 8 2010 Problem 12
AMC8 2010 年第 12 题
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Of the 500 balls in a large bag, 80% are red and the rest are blue. How many of the red balls must be removed so that 75% of the remaining balls are red?
一个大包里的 500 个球中，有 80％是红球，其他是蓝球。需要从包中移走多少红球，使得包中剩下的球中，75％是红球？
- A.25
- B.50
- C.75
- D.100
- E.150
正确答案 · Correct Answer
D
解析 · Solution
Solution 1
Before any balls are taken out of the bag, there are 400 red balls. Let the number of red balls we take out of the bag be . Since we want the number of red ball to be 75% of the remaining balls, we can set up the equation: 0.75(500–x)=400–x. In words, 75% of the total remaining balls are equal to the remaining red balls. Solving we get x=100, so our answer is 100..L.L Video by MathTalks https:
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