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胖博士奥数课堂707期：20200229（五年级）比例问题视频讲解
一个口袋里装有一些小球，其中红球与总数的比是5:12。又放进18个红球，这时红球占现在总数的2/3。现在共有小球多少个？
胖博士奥数课堂32/274
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