GMAT
题目
A water pump began filling an empty swimming pool with water and ran at a constant rate tillì the swimming pool was full. At sometime, the pool was full, and hours later, it was full. How many hours would it take the pump to fill the empty pool completely?
解析
答案：(C)
\(2\frac{1}{3}\) 小时可改写为 \(\frac{7}{3}\) 小时。
\(\frac{7}{3}\) 小时内注入的水量 = \(\frac{5}{6} - \frac{1}{2} = \frac{1}{3}\)
→ 每小时注入的水量 = \(\frac{1/3}{7/3} = \frac{1}{7}\)
\(w = r \times t\)
→ \(t = \frac{w}{r} = \frac{1}{1/7} = 7\) 小时
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