[求助]请问一题PP2-DS#179

candace1008

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~

binggerg

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

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

kelly41099

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

from (1) --> 1/x

from (2) ---> 1/y

(1)+(2) together  ----> C

苹果梨

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

huangxiuying

同意LS的,选D

iamsean

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

candace1008

谢谢各位~感激不尽

kpkinda

应该是D，同意楼上