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time and work

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time and work

by anjaligeorge1 » Thu Jun 12, 2008 9:40 am
Pump X started filling an empty pool with water and continued at a constant rate. 5 hours later, the pool was 1/4 full. Then, pump B joined the work. 9 hours later, the pool was full. Working alone at its constant rate, how long will it take B to fill the empty pool?

(A) 15
(B) 18
(C) 20
(D) 30
(E) 45

answer is D.How do i solve this
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Re: time and work

by durgesh79 » Thu Jun 12, 2008 9:52 am
anjaligeorge1 wrote:Pump X started filling an empty pool with water and continued at a constant rate. 5 hours later, the pool was 1/4 full. Then, pump B joined the work. 9 hours later, the pool was full. Working alone at its constant rate, how long will it take B to fill the empty pool?

(A) 15
(B) 18
(C) 20
(D) 30
(E) 45

answer is D.How do i solve this
Pump X fills 1/4 of the Pool in 5 hrs. Means it'll take 4X5=20 hrs for X to fill the total pool alone.

Both X and Y fill 3/4 of the pool in 9 hrs. Mean it'll take 9*4/3 = 12 hrs for both X and Y to fill the total pool.

1/Y + 1/20 = 1/12

Y = 30. Option D
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