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标题: [求助]请问一题PP2-DS#179 [打印本页]

作者: candace1008 时间: 2008-5-27 20:41
标题: [求助]请问一题PP2-DS#179

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 ?

(1) Working alone at its constant rate, pump X would have taken 80 minutes to fill the tank with water.

(2) Working alone at its constant rate, pump Y would have taken 120 minutes to fill the tank with water.

请帮帮我解答~

作者: binggerg 时间: 2008-5-27 22:01

1(1/x+1/y)=48

ask for (1/x)/(1/y)

作者: kelly41099 时间: 2008-5-28 01:12

ask for 1/x/(1/x+1/y).

from (1) --> 1/x

from (2) ---> 1/y

(1)+(2) together ----> C

作者: 苹果梨 时间: 2008-5-28 09:18

这个题我觉得选D，（1）1/x=1/80 (2)1/y=1/120 这样就可应把另一个求出来了，是单独能得到答案的

作者: huangxiuying 时间: 2008-5-29 08:03
同意LS的,选D

作者: iamsean 时间: 2008-5-29 08:58

同意LS还有再LS的，每个条件都可以单独求出答案。

可以认为题目中有3个未知数：pump x的速度, pump y的速度, 还有tank的容量，问题求其中两个未知数的比例，所以只需要两个方程。题目本身给了一个，条件再有一个就够了

作者: candace1008 时间: 2008-5-30 08:42

谢谢各位~感激不尽

作者: kpkinda 时间: 2008-5-30 21:11

应该是D，同意楼上

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