5 collectors have some rare collection, then comes the 6th collector with 50 pieces of collection, and then the average piece of collection is 5 more than the average before

题目

5 collectors have some rare collection, then comes the 6^th collector with 50 pieces of collection, and then the average piece of collection is 5 more than the average before. Then comes the 7^th collector with some collection, and the average is 5 more than the average of the first 6 collectors. How many pieces of collection does the 7^th collector have?

选项

解析

设5位收藏家的平均收藏数为\(x\)，则总数为\(5x\)。已知条件： \(5x + 60 = 6(x + 5)\) 解得\(x = 20\) 6位收藏家的总数 = \((20 + 5)×6 = 150\) 7位收藏家的总数 = \((25 + 5)×7 = 210\) 因此，第7位收藏家的收藏数 = \(210 - 150 = 60\) 选项B

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