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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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Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t  [#permalink]

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New post 12 Mar 2015, 06:52
1
1
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A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

90% (01:17) correct 10% (01:29) wrong based on 104 sessions

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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t  [#permalink]

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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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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t  [#permalink]

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New post 12 Mar 2015, 09:05
1
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]

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New post 13 Mar 2015, 13:41
1
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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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t  [#permalink]

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New post 14 Mar 2015, 08:04
1
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


Kudos for a correct solution.

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Re: Pump X takes 28 hours to fill a pool. Pump Y takes 21 hours to fill t  [#permalink]

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New post 15 Mar 2015, 22:17
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 3181 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]

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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]

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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


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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]

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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


Kudos for a correct solution.


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] 26 May 2019, 02:49
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