Bunuel wrote:
Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill the same pool. How long does it take them to fill the same pool if they are working simultaneously?
A. 7 hr
B. 10 hr
C. 12 hr
D. 14 hr
E. 18 hr
Kudos for a correct solution.
28x = 21y = (x+y)k, we have to find k.
x/y=21/28
Now Considering equation 21y = (x+y)k, putting x/y=21/28
we get k=12, so 12 hours. C
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