GMAT
题目
Water flows into an empty tank of 54 liters via 12 small pipes. The rate of flow in each pipe is 1 liter per hour. However, water also flows out of the tank via several large pipes at the rate of 1.5 liter per hour per pipe. If the tank is completely full after 12 hours, how many large pipes are there?
解析
水箱12小时注满，因此**实际净流入量**需为\( \frac{54}{12} = 4.5 \)升/小时。
当前**标称流入量**为12升/小时，流出量未知。
用标称流入量减去实际净流入量，可得流出量：\( 12 - 4.5 = 7.5 \)升/小时。
已知每条大型出水管的流量为1.5升/小时，因此所需出水管数量为：\( \frac{7.5}{1.5} = 5 \)。
答案：D
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