PP-DS-Test1-179

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179. 17563-!-item-!-187;#058&011544
Working independently at their respective constant rates, pumps X and Y took 48 minutes to fill an empty tank with water. What fraction of the water in the full tank came from pump X ?
不確定是這樣算嗎? 不過應該是吧?
(1) Working alone at its constant rate, pump X would have taken 80 minutes to fill the tank with water.
1/80 + 1/Y = 1/48 算出得Y=120

80/(80+120) = 40% sufficient

(2) Working alone at its constant rate, pump Y would have taken 120 minutes to fill the tank with water.
1/X + 1/120 = 1/48 得X=80

80/(80+120) = 40% sufficient

Answer : D