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题库 / OG2017Q-DS-186
How many hours would it take Pump A and Pump B working together, each at its own constant rate, to empty a tank that was initially full?
(1) Working alone at its constant rate, Pump A would empty the full tank in 4 hours 20 minutes.
(2) Working alone, Pump B would empty the full tank at its constant rate of 72 liters per minute.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
题目分析：
花费的时间 = 油箱的体积 / (泵A抽油的速度 + 泵B抽油的速度)
（1） 泵A单独工作，抽空油箱需要4小时20分钟，仅此条件可以得到A抽油的速度。
（2） 泵B单独工作，抽油的速度为72升/分钟。
综合条件1和条件2，由于条件1不能得到泵A每分钟抽取多少升，也不能得到油箱的体积，因此，无法计算得到泵A和泵B一起工作抽空油箱的时间。
因此，本题答案为（E），两个条件结合也无法说明问题，需要添加新数据。
这题阅读的时候容易粗心。条件1给的是时间，条件2给的是速度。因此两个条件together还是无法求解。
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