There are 30 marbles with the same size in a box,in which th

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There are 30 marbles with the same size in a box,in which there are 10 red ones,8 white ones,7 yellow ones and 5 green ones.How many marbles should be taken out at least at a time so as to make sure there are 7 marbles with the same color without opening eyes

24次
两种想法：
1、如果每次取的颜色都不同,每个球取5次共取 5×4=20个,绿色已经取光了,还剩3种颜色,接着每个颜色取1次,3×1=3.最后只要再去1次,不论取出三种颜色的哪一种,都能保证有7个球颜色相同,所以有一共是20+3+1=24次.
第二种想法.
有5次把绿球都取光了,剩下的球只是三种颜色,每种颜色的球取6次,即6×3=18,然后再取一次就能保证有7个球颜色相同,所以有一共是5+18+1=24次.

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