Pipe A runs 30 liters of water per minute into a pool that h

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BTGmoderatorAT: Moderator; Posts: 426; Joined: Tue Aug 22, 2017 8:48 pm; Followed by:1 members

Pipe A runs 30 liters of water per minute into a pool that h

by BTGmoderatorAT » Thu Nov 09, 2017 4:33 pm

Pipe A runs 30 liters of water per minute into a pool that has a total volume of 3,600 liters. Pipe B fills a third of the pool in 6 hours.

Working together how long will it take both pipes to fill the pool?

A. 2 hours and 36 minutes
B. 1.5 hours
C. 9 hours and 12 minutes
D. 15 hours
E. 1 hour and 48 minutes.

OA: E

Is there a strategic approach to this question?

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Source: Beat The GMAT — Problem Solving | Thu Nov 09, 2017 4:33 pm

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Jay@ManhattanReview: GMAT Instructor; Posts: 3008; Joined: Mon Aug 22, 2016 6:19 am; Location: Grand Central / New York; Thanked: 470 times; Followed by:34 members

by Jay@ManhattanReview » Thu Nov 09, 2017 9:18 pm

ardz24 wrote:Pipe A runs 30 liters of water per minute into a pool that has a total volume of 3,600 liters. Pipe B fills a third of the pool in 6 hours.

Working together how long will it take both pipes to fill the pool?

A. 2 hours and 36 minutes
B. 1.5 hours
C. 9 hours and 12 minutes
D. 15 hours
E. 1 hour and 48 minutes.

OA: E

Is there a strategic approach to this question?

For pipe A, at the rate of 30 lit/min, it will take 3600/30 = 120 min = 2 hours, working individually, to fill the pool.
Since Pipe B fills one-third of the pool in 6 hours, it will take 6*3 = 18 hours, working individually, to fill the pool.

Working together, both the pipes will fill 1/2 + 1/18 = 5/9 part of the pool in an hour.

Thus, it will take both the pipes will take 9/5 = 1 hr 48 min. to fill the pool.

The correct answer: E

Hope this helps!

-Jay
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Manhattan Review GMAT Prep

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pm; Location: Vancouver, BC; Thanked: 5254 times; Followed by:1268 members; GMAT Score:770

by Brent@GMATPrepNow » Fri Nov 10, 2017 8:45 am

ardz24 wrote:Pipe A runs 30 liters of water per minute into a pool that has a total volume of 3,600 liters. Pipe B fills a third of the pool in 6 hours.

Working together how long will it take both pipes to fill the pool?

A. 2 hours and 36 minutes
B. 1.5 hours
C. 9 hours and 12 minutes
D. 15 hours
E. 1 hour and 48 minutes.

Let's determine the COMBINED RATE of the two pipes

Given: Pipe A's RATE = 30 liters per minute
This is equivalent to 1800 liters per HOUR

Pipe B fills a third of the pool in 6 hours
So, Pipe B fills the ENTIRE pool (3600 liters) in 18 hours
Rate = Output/time
= 3600/18
= 200 liters per hour

COMBINED RATE = 1800 + 200
= 2000 liters per hour

Working together how long will it take both pipes to fill the pool?
Time = output/rate
= 3600/2000
= 36/20 hours
= 9/5 hours
= 1 4/5 hours
= 1 hour and 48 minutes
= E

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Sun Nov 03, 2019 7:33 pm

BTGmoderatorAT wrote:Pipe A runs 30 liters of water per minute into a pool that has a total volume of 3,600 liters. Pipe B fills a third of the pool in 6 hours.

Working together how long will it take both pipes to fill the pool?

A. 2 hours and 36 minutes
B. 1.5 hours
C. 9 hours and 12 minutes
D. 15 hours
E. 1 hour and 48 minutes.

OA: E

Is there a strategic approach to this question?

The combined rate of pipes A and B is:

30/(1/60) + (1/3 x 3600)/6 = 1800 + 1200/6 = 1800 + 200 = 2000 liters per hour.

Thus, it will take 3600/2000 = 36/20 = 9/5 = 1 4/5 hours = 1 hour and 48 minutes to fill the pool when the two pipes work together.

Alternate Solution:

Pipe A's rate is 30 liters per minute, or 1800 liters per hour. Pipe B's rate is 1,200 liters in 6 hours, or 200 liters per hour. Thus, their combined hourly rate is 1800 + 200 = 2000 liters.

Thus, it will take 3600/2000 = 36/20 = 9/5 = 1 4/5 hours = 1 hour and 48 minutes to fill the pool when the two pipes work together.

Answer: E

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