OG上有这样一道题：A marketing firm dertermined that,of 200 households surveryed,80 used neither Brand A nor Brand B soap,60 used only Brand A soap,and for every household that used both brands of soap,3 used only Brand B sop.How many of the 200 households used both brands of soap?解释中说“3 used only Brand B soap”是3倍的意思，我原以为是其中的3个的意思，为什么是3倍的含义呢？谢谢！
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发表于 2014-9-8 09:09:11
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