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A pond has an inlet to fill it up and an outlet to drain it.

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Director
Joined: 20 Aug 2007
Posts: 851
Location: Chicago
Schools: Chicago Booth 2011
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A pond has an inlet to fill it up and an outlet to drain it. [#permalink]

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27 Feb 2008, 18:15
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

A pond has an inlet to fill it up and an outlet to drain it. The inlet can fill it in 5 hours and the the outlet can drain it in 8 hours. Suppose the pond was empty and the person in charge of filling it up opened the inlet but forgot to close the outlet. After 4 hours, he realized that the outlet is still open. At that time, he closed the outlet. How long did it take for the pond to get filled after the outlet was closed?

a) 5
b) 4
c) 3.5
d) 7
e) 8
Intern
Joined: 25 Feb 2008
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Kudos [?]: 1 [1] , given: 0

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27 Feb 2008, 19:30
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sonibubu wrote:
A pond has an inlet to fill it up and an outlet to drain it. The inlet can fill it in 5 hours and the the outlet can drain it in 8 hours. Suppose the pond was empty and the person in charge of filling it up opened the inlet but forgot to close the outlet. After 4 hours, he realized that the outlet is still open. At that time, he closed the outlet. How long did it take for the pond to get filled after the outlet was closed?

a) 5
b) 4
c) 3.5
d) 7
e) 8

after 4hrs = 80% - 50% = 30% filled
100% takes = 5 hr remaining => 70% takes 3.5 hours
CEO
Joined: 29 Mar 2007
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28 Feb 2008, 06:13
sonibubu wrote:
A pond has an inlet to fill it up and an outlet to drain it. The inlet can fill it in 5 hours and the the outlet can drain it in 8 hours. Suppose the pond was empty and the person in charge of filling it up opened the inlet but forgot to close the outlet. After 4 hours, he realized that the outlet is still open. At that time, he closed the outlet. How long did it take for the pond to get filled after the outlet was closed?

a) 5
b) 4
c) 3.5
d) 7
e) 8

C? this question was kinda confusing cause I thought it was asking for the total time.

Anyway. 4*1/5 = 4/5 4*1/8 ---> 1/2 --> 4/5-1/2=3/10

so we have 7/10 remaining.

Now its just 7/10/1/5 --> 35/10 = 3.5
Re: pool drain   [#permalink] 28 Feb 2008, 06:13
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