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One pump drains one-half of a pond in 3 hours, and then a second pump

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One pump drains one-half of a pond in 3 hours, and then a second pump  [#permalink]

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New post 17 Jun 2019, 00:15
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Question Stats:

55% (02:08) correct 45% (02:03) wrong based on 94 sessions

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One pump drains one-half of a pond in 3 hours, and then a second pump starts draining the pond. The two pumps working together finish emptying the pond in one-half hour. How long would it take the second pump to drain the pond if it had to do the job alone?

A. 1 hour
B. 1.2 hour
C. 3 hours
D. 5 hours
E. 6 hours

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One pump drains one-half of a pond in 3 hours, and then a second pump  [#permalink]

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New post 17 Jun 2019, 01:21
P1 can drain the full pond in 6 hours.

Rate of P1 (w/t) + Rate of P2 = rate of both together.
1pond in 6 hrs + 1pond in p2 hrs= 1pond in 1 hr(1/2hrs - half pond)
1/6+1/P2=1; so 5P2=6hrs and p2= 1.2 hrs

IMO B

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Re: One pump drains one-half of a pond in 3 hours, and then a second pump  [#permalink]

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New post 22 Jun 2019, 01:34
what does 'The two pumps working together finish emptying the pond in one-half hour' mean??
1. It takes 1/2hr to empty the full tank.
or
2. It takes 1/2hr to empty 1/2 tank. (If this interpretation is correct please explain)
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Re: One pump drains one-half of a pond in 3 hours, and then a second pump  [#permalink]

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New post 22 Jun 2019, 01:49
Ayushpandiya wrote:
what does 'The two pumps working together finish emptying the pond in one-half hour' mean??
1. It takes 1/2hr to empty the full tank.
or
2. It takes 1/2hr to empty 1/2 tank. (If this interpretation is correct please explain)

Second one is correct as the question says “finish emptying“

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One pump drains one-half of a pond in 3 hours, and then a second pump  [#permalink]

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New post Updated on: 25 Oct 2019, 12:14
Bunuel wrote:
One pump drains one-half of a pond in 3 hours, and then a second pump starts draining the pond. The two pumps working together finish emptying the pond in one-half hour. How long would it take the second pump to drain the pond if it had to do the job alone?

A. 1 hour
B. 1.2 hour
C. 3 hours
D. 5 hours
E. 6 hours


in 3 1/2 hours P1 can drain 7/2*1/6=7/12 of pond
so P2 can drain 1-(7/12)=5/12 of pond in one-half hour,
or a rate of 10/12 of pond in one hour
1 pond/(10/12) rate=1.2 hours time for P2 to drain pond alone
B

Originally posted by gracie on 22 Jun 2019, 19:16.
Last edited by gracie on 25 Oct 2019, 12:14, edited 1 time in total.
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Re: One pump drains one-half of a pond in 3 hours, and then a second pump  [#permalink]

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New post 25 Oct 2019, 06:14
Bunuel wrote:
One pump drains one-half of a pond in 3 hours, and then a second pump starts draining the pond. The two pumps working together finish emptying the pond in one-half hour. How long would it take the second pump to drain the pond if it had to do the job alone?

A. 1 hour
B. 1.2 hour
C. 3 hours
D. 5 hours
E. 6 hours


rt=j; r_a(3)=0.5 job…r_a=1/6;
(r_a+r_b)(0.5)=0.5 job, r_a+r_b=1, r_b=1-1/6=5/6;
r_b(t)=1 job…t=1/r_b…t=1/5/6=6/5=1.2 hrs

Answer (B)
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Re: One pump drains one-half of a pond in 3 hours, and then a second pump   [#permalink] 25 Oct 2019, 06:14
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One pump drains one-half of a pond in 3 hours, and then a second pump

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