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Pumps A, B and C operate at their respective constant rates. [#permalink]
 16 Feb 2006, 11:59
Question Stats:
80% (01:28) correct
20% (06:07) wrong based on 4 sessions
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
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Manager
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1/a + 1/b = 5/6
1/b +1/c = 2/3
1/c + 1/a =1/2
add all of them together u get
1/a +1/b +1/c = 1
hence they can fill the tank in 1 hr
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GMAT Club Legend
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1/A + 1/B = 5/6 -- (1)
1/A + 1/C = 2/3 -- (2)
1/B + 1/C = 1/2 -- (3)
(1) - (2)
1/B - 1/C = 1/6 --(3)
1/B + 1/C = 1/2 --(2)
(3) + (2)
2/B = 2/3
1/B = 1/3
1/3 + 1/C = 1/2
1/C = 1/6
1/A + 1/6 = 2/3
1/A = 1/2
1/A + 1/B + 1/C = 1
A + B + C = 1 hour
Ans E
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Re: Pumps A, B and C operate at their respective constant rates. [#permalink]
09 Dec 2011, 04:12
Rate of A + B = 5/6---------(i) Rate of A + C = 2/3 --------(ii) Rate of B + C = 1/2 --------(iii) Adding (i), (ii) and (iii) Together 2(A + B +C) = 12/6 = 1 A, B and C took 1 hour. Ans. E
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Manager
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Re: Pumps A, B and C operate at their respective constant rates. [#permalink]
13 Mar 2012, 02:50
Could someone explain why we use the reciprocal here?
Thanks, alot!
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Re: Pumps A, B and C operate at their respective constant rates. [#permalink]
13 Mar 2012, 03:00
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Re: Pumps A, B and C operate at their respective constant rates.
[#permalink]
13 Mar 2012, 03:00
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