Two hoses (X and Y) are filling a pool

题目

Two hoses (X and Y) are filling a pool. Working alone at their individual constant rates, Hose X could fill the pool in 6 hours and Hose Y could do it in 4 hours. If the two hoses work together to fill half the pool, and then Hose Y finishes alone, how long will it take to fill the pool?

选项

2 hours, 48 minutes

3 hours

3 hours, 12 minutes

3 hours, 24 minutes

3 hours, 48 minutes

解析

设泳池的容量为12单位。 - X水管的效率为2单位/小时，Y水管的效率为3单位/小时。 - X、Y水管的合效率为5单位/小时。注满泳池一半（6单位）所需的时间为：\( 6÷5 = 1 \)小时12分钟。此时还剩6单位的注水量，由Y水管单独完成所需的时间为：\( 6÷3 = 2 \)小时。因此，注满整个泳池的总时间为3小时12分钟，答案是（C）

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