填空题 You are trying to fill a bath with both taps on, but have accidentally left out the plug. Normally the hot water tap takes 8 minutes to fill the bath and the cold water tap takes 10 minutes. However, the water empties out through the plug hole in 5 minutes. How long will it take for the bath to fill?
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【正确答案】 1、40 minutes.    
【答案解析】设浴缸容量为x，n为三管一起开的充满水的时间，热水充满浴缸要8分钟，所以每分钟充满x/8，同理冷水每分钟充满x/10，而放水管每分钟放水x/5，故可列方程(x/8+x/10-x/5)×n=x，解得n=40，即需40分钟。