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SammyJaggi: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Tue Nov 27, 2012 4:08 am

by SammyJaggi » Tue Nov 27, 2012 4:10 am

Pipe A can fill a pool in 5 days and pipe B can fill the pool in 3 days .if they start working together at same time,how long(in hours) will it take to fill the pool. if pipe B stops working after a DAy??

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Source: Beat The GMAT — Problem Solving | Tue Nov 27, 2012 4:10 am

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Tue Nov 27, 2012 4:40 am

SammyJaggi wrote:Pipe A can fill a pool in 5 days and pipe B can fill the pool in 3 days .if they start working together at same time,how long(in hours) will it take to fill the pool. if pipe B stops working after a DAy??

In one day A fills 1/5 of the pool and B fills 1/3 of the pool.
Hence, in one day together they fill (1/5 + 1/3) = 8/15 of the pool

Hence, after one day, (1 - 8/15) = 7/15 of the pool is empty which should be filled by A.

A takes 5 days to fill the entire pool.
Hence, to fill 7/15 of the pool A will take (7/15)*5 days = 7/3 days = (7/3)*24 hours = 56 hours

Hence, it will take (24 + 56) hours = 80 hours to fill the tank.

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nisagl750: Master | Next Rank: 500 Posts; Posts: 145; Joined: Tue Jan 31, 2012 6:50 amFollowed by: 2 members; Location: New Delhi; Thanked: 16 times; GMAT Score:760

by nisagl750 » Tue Nov 27, 2012 4:45 am

SammyJaggi wrote:Pipe A can fill a pool in 5 days and pipe B can fill the pool in 3 days .if they start working together at same time,how long(in hours) will it take to fill the pool. if pipe B stops working after a DAy??

Pipe A can fill pool in 5 days
In one day Pipe A can fill = 1/5 = 3/15 (multiply by 3 on Nr and Dr)

Similarly,
In one day Pipe B can fill = 1/3 = 5/15 (multiply by 3 on Nr and Dr)

Together in one day they can fill = 3/15 + 5/15 = 8/15 of pool....

Remaining = 1-8/15 = 7/15
Since Pipe B stops working after 1 day, Pipe A has to fill 7/15 of pool alone (awwww....Poor Pipe A)
So Pipe A will take = (7/15)/(3/15) = 7/3 Days

So total no. of days req to fill the pool is = 1 + 7/3 = 10/3 Days

Remember, We have to find no. of hours....not no. of days..(multiply by 24)

So, No. of hours = 80Hrs

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Tue Nov 27, 2012 5:35 am

SammyJaggi wrote:Pipe A can fill a pool in 5 days and pipe B can fill the pool in 3 days .if they start working together at same time,how long(in hours) will it take to fill the pool. if pipe B stops working after a DAy??

Let the pool = 15 units.

Rate for A = w/t = 15/5 = 3 units per day.
Rate for B = w/t = 15/3 = 5 units per day.
Work produced by A and B in one day = 3+5 = 8 units.
Time for A to fill the remaining 7 units = w/r = 7/3 days = (7/3)(24 hours) = 56 hours.
Total time = one day + 56 hours = 24+56 = 80 hours.

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