PP P1-PS-191

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PP P1-PS-191

文章jason2532 » 2010-04-06 16:59

想請問一下這題如何算? 謝謝!

191. Pumps A,B,and C operate at their respective constant rates. Pumps A and B, operating simultaneously, can fill a certain tank in 6/5 hours; pumps A and C, operating simultaneously, can fill the tank in 3/2 hours; and pumps B and C, operating simultaneously, can fill the tank in 2 hours. How many hours does it take pumps A,B, and C, operating simultaneously, to fill the tank?
(A)1/3
(B)1/2
(C)2/3
(D)5/6
(E)1
正確答案是(E)
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註冊時間: 2010-03-18 17:55

Re: PP P1-PS-191

文章sunnyblue13s » 2010-07-08 01:48

1/(1/x+1/y) = 6/5 => (1/x+1/y) = 5/6

1/(1/y+1/z) = 3/2 => (1/y+1/z) = 2/3

1/(1/x+1/z) = 2 => (1/x+1/z) = 1/2

(1/x+1/y+1/z) = 上述三者相加/2

Ans = 1/(1/x+1/y+1/z) = 1/1 =1 hr
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