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 min

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问题 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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答案40 minutes.

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。)  
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