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Water pumps...

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by smallsorrow » Thu Oct 09, 2008 12:14 am
Two water pumps, working similar at their respective constant rates, took exactly 4 hours to fill a pool. If the rate of pump1 is 1.5 times the rate of the other, how many hours would it have taken the fastest pump to fill the pool if it worked alone?

A)5
B)16/3
C)11/2
D)2
E)20/3
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by Mani_mba » Thu Oct 09, 2008 12:34 am
If pump1 works alone, it takes x hours to fill the pool
If pump2 works alone, it would take 3/2x hours to fill the pool.

1/x + 2/3x = 1/4

5/3x = 1/4

x = 20/3.

IMO E.
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by vivek.kapoor83 » Thu Oct 09, 2008 10:22 am
IMO 20/3
Let 100 ltr of tank to be filled.
suppose Pump b fills =10 ltr/hr & 1 fills= 15ltr/hr(As per ques)
total they can fill =25 ltr/hr
25*4 =100 ltr full tank,
So A will take - 100/15 = 20/3


This is the strange way of solving it..but i always do Work Rate prob like this and my accuracy is 100%
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by earth@work » Fri Oct 10, 2008 4:34 pm
yeah...20/3
Let rates be R & r...R+r = 4 hrs
given R=1.5r...... r +1.5r=2.5r=4hrs
r=4*2.5 hrs i.e smaller pipe will take 4*2.5hrs
Pipe R (=1.5r) will take = 4*2.5/1.5=20/3
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