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A pool has two inlet pipes. The first inlet can fill the

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A pool has two inlet pipes. The first inlet can fill the [#permalink] New post 27 Feb 2008, 18:10
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A pool has two inlet pipes. The first inlet can fill the pool in 6 hours, the other can fill it in 4 hours. If the first pipe is open for 2 hours and then the second is open. How long will take for the pool to be filled after the second pipe is open?
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Re: Rate problem [#permalink] New post 27 Feb 2008, 19:38
first inlet fills 1/3 after 2 hours. To fill = 2/3rds.
new effective rate = (6*4)/(6+4) = 2.4
if 100% = 2.4 what is (100 * 2/3)% = ?

= 2.4 * 2 /3 = 1.6 hours
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Re: Rate problem [#permalink] New post 27 Feb 2008, 20:41
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sonibubu wrote:
A pool has two inlet pipes. The first inlet can fill the pool in 6 hours, the other can fill it in 4 hours. If the first pipe is open for 2 hours and then the second is open. How long will take for the pool to be filled after the second pipe is open?



1. After 2 hours working, first inlet filled = 2*1/6 = 1/3 the pool

2. When 2 inlets opened together, they must filled the remaining pool = 2/3 job

3. 1/6 + 1/4 = 2/(3*X) or X = 1.6h
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Re: Rate problem [#permalink] New post 27 Feb 2008, 20:57
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Please someone help me out by providing fully explained answer of this question.
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Re: Rate problem [#permalink] New post 28 Feb 2008, 06:22
sonibubu wrote:
A pool has two inlet pipes. The first inlet can fill the pool in 6 hours, the other can fill it in 4 hours. If the first pipe is open for 2 hours and then the second is open. How long will take for the pool to be filled after the second pipe is open?



First pump runs for 2 hours. its rate is 1pool/6hours. Thus 2(1/6)= 1/3

1-1/3 = 2/3 of the pool remaining.


thus now just add the rates. 1/6+1/4 --> 5/12

(2/3)/(5/12) --> 8/5 or 1hr and 36 minutes.
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Re: Rate problem [#permalink] New post 28 Feb 2008, 06:43
sonibubu wrote:
A pool has two inlet pipes. The first inlet can fill the pool in 6 hours, the other can fill it in 4 hours. If the first pipe is open for 2 hours and then the second is open. How long will take for the pool to be filled after the second pipe is open?


1) First pipe open for 2 hours, thus 2 hours / 6 hours = 1/3 of the pool is filled.

Whole pool = 3/3 - 1/3 already filled = 2/3 left to be filled.

2. Second pipe is opened. Two pipes working together = 1/6 + 1/4. Common denominator = 4/24 + 6/24 = 10/24.

Factoring down 10/24, result is 5/12. This is now the rate of the two pipes working together.

To complete, take amount of pool left to be filled (2/3) divided by the rate (5/12).

(2/3) / (5/12) translates into (2/3) x (12/5) = 24/15, or 8/5.

Question asks how long it take to fill the rest of the pool after the second pipe is opened.

Answer is 1 3/5, or 1.6 hours.
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Re: Rate problem [#permalink] New post 29 Feb 2008, 06:32
Nice job. 1.6 hrs is correct.
Re: Rate problem   [#permalink] 29 Feb 2008, 06:32
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