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the pump needs

by sanju09 » Mon Apr 26, 2010 6:08 am
A pump can be operated both for filling a tank and for emptying it. The capacity of tank is 2400 cubic foot, the emptying capacity of the pump 10 cubic foot per minute higher than its filling capacity. Consequently the pump needs 8 minutes less to empty the tank than to fill it. What is the filling capacity of the pump, in cubic foot per minute?
(A) 50
(B) 52
(C) 55
(D) 60
(E) 63
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by liferocks » Mon Apr 26, 2010 6:57 am
Let the filling capacity of the pump be x cubic foot per minute
so
8x/10=2400/(x+10)
or x^2+10x-3000=0
or (x+60)(x-50)=0
hence x=50 as the ans is positive

ans option A
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by Fiver » Mon Apr 26, 2010 8:52 pm
Agree with A.
Here's another approach:

10 extra contributed across the emptying time (et) is the same as what the filling rate (f) could do in 8 mins.
Hence 10 * et = 8 * f
et = 4/5 * f
Given et = f + 10
Hence (f + 10) * 4/5* f = 2400
(f+10) * f = 3000
60 * 50 = 3000
Hence f = 50
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