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Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t

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Bunuel
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Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink] New post   12 Mar 2015, 06:52
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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


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C
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23a2012
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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink] New post   12 Mar 2015, 07:23
the answer is C
Pump X takes 28 hours to fill a pool, so X rates is 1/28

Pump Y takes 21 hours to fill a pool, so Y rates is 1/21

working togther=(1/21+1/28)*t=1
7/84*t=1
t=84/7 =14
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chetan2u
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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink] New post   12 Mar 2015, 09:05
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23a2012 wrote:
the answer is C
Pump X takes 28 hours to fill a pool, so X rates is 1/28

Pump Y takes 21 hours to fill a pool, so Y rates is 1/21

working togther=(1/21+1/28)*t=1
7/84*t=1
t=84/7 =14


hi,
ans C..
1/21+1/28=7/84..
time taken =84/7=12...
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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink] New post   13 Mar 2015, 13:41
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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


Short and quick approach for this type of questions is :

\(\frac{A X B}{A + B}\)

--> \(\frac{28 X 21}{28 + 21}\)

= 12 ans

Hence C

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SG :wink:
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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink] New post   14 Mar 2015, 08:04
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1/28+ 1/21 = 1/12

Simultaneous working= 12.

Answer C.

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


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Bunuel
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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink] New post   15 Mar 2015, 22:17
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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.


MAGOOSH OFFICIAL SOLUTION:

Express the rates of pumps in terms of (pools/hours). Pump X operates at rate of 1/28, and pump Y operates at 1/21. When the pumps work together, we add the rates.
Attachment:
wp_img10.png
wp_img10.png [ 4.43 KiB | Viewed 7766 times ]


So, combined, the pumps operate at a rate of 1/12, which means they can fill a pool in 12 hr.

Answer = (C)
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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink] New post   17 Mar 2015, 03:27
Combined rate \(= \frac{1}{21} + \frac{1}{28} = \frac{1}{12}\)

Time required = 12 Hours

Answer = C
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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink] New post   25 May 2019, 05:26
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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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink] New post   26 May 2019, 02:49
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


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comined rate ; 1/21+1/28 = 58/49 ; 12 hrs
IMO C
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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink] New post   28 Apr 2020, 08:15
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.


Given:
1. Pump X takes 28 hours to fill a pool.
2. Pump Y takes 21 hours to fill the same pool.

Asked: How long does it take them to fill the same pool if they are working simultaneously?

In 1 hour Pump X fills = 1/28 of the pool
In 1 hour Pump Y fills = 1/21 of the pool
In 1 hour Pump X & Pump Y fill = 1/28 + 1/21 = (3 + 4)/84 = 7/84 = 1/12 of the pool
Number of hours Pump X & Pump Y will take = 12 hours to fill the pool

IMO C
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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t [#permalink]
28 Apr 2020, 08:15
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