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Almasha: Newbie | Next Rank: 10 Posts; Posts: 5; Joined: Mon Oct 17, 2011 5:43 am

by Almasha » Wed Oct 19, 2011 6:19 am

IF 4 men OR 7 boys can do a work in 29 days how much time will 12 men AND 8 boys take?
???

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Source: Beat The GMAT — Problem Solving | Wed Oct 19, 2011 6:19 am

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 amFollowed by: 21 members; Thanked: 230 times

by shankar.ashwin » Wed Oct 19, 2011 6:25 am

Work done by 1 man in 1 day - 1/(29*4)
Work done by 1 boy in 1 day - 1/(29*7)

Together 12 men and 8 boys will do 12/(29*4) + 8/(29*7) (or) 1/7 work in 1 day.

Hence they will require 7 days to complete the job.

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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 » Wed Oct 19, 2011 6:27 am

Almasha wrote:IF 4 men OR 7 boys can do a work in 29 days how much time will 12 men AND 8 boys take?

4 men can do the work in 29 days.
Hence, one man in one day does 1/(4*29) of the work
Hence, 12 men in one day do 12/(4*29) of the work

7 boys can do the work in 29 days.
Hence, one boy in one day does 1/(7*29) of the work
Hence, 8 boys in one day do 8/(7*29) of the work

Hence, 12 men and 8 boys in one day do [12/(4*29) + 8/(7*29)] = [(12*7 + 4*8)/(4*7*29)] = [4(3*7 + 8)/(4*7*29)] = [4*29/(4*7*29)] = 1/7 of the work

Hence, 12 men and 8 boys will finish the work in 7 days.

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neelgandham: Community Manager; Posts: 1060; Joined: Fri May 13, 2011 6:46 amFollowed by: 52 members; Location: Utrecht, The Netherlands; Thanked: 318 times

by neelgandham » Wed Oct 19, 2011 6:31 am

IF 4 men OR 7 boys can do a work in 29 days how much time will 12 men AND 8 boys take?

4 men can complete a work in 29 days
12 men can complete it in 29*4/12 = 29/3 days

7 boys can complete a work in 29 days
8 boys can complete it in 29*7/8 days

In 1 day, 12 men can complete (3/29)th of the work
In 1 day, 7 boys can complete (8/(7*29))th of the work

Total work completed on a given day = (3/29) + (8/(7*29)) = 1/7

In one day, 1/7 of the work is done. So it would take 7 days for 12 men AND 8 boys to complete the work !

Anil Gandham
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
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Almasha: Newbie | Next Rank: 10 Posts; Posts: 5; Joined: Mon Oct 17, 2011 5:43 am

by Almasha » Wed Oct 19, 2011 6:44 am

Everybody is taking it as tough.. thats why i am feeling like "confused" after getting many responses.

I am not getting over it..

:!:

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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 » Wed Oct 19, 2011 7:19 am

Almasha wrote:IF 4 men OR 7 boys can do a work in 29 days how much time will 12 men AND 8 boys take?
???

Plug in numbers so that the rate for 4 men = the rate for 7 boys.

Let the rate for each man = 7 units per day.
Rate for 4 men = 4*7 = 28 units per day.

Let the rate for each boy = 4 units per day.
Rate for 7 boys = 7*4 = 28 units per day.

Work completed by each group in 29 days = r*t = 28*29 units.

Combined rate for 12 men and 8 boys = (12*7) + (8*4) = 116 units per day.
Time to complete the job = w/r = (28*29)/116 = 7 days.

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user123321: Master | Next Rank: 500 Posts; Posts: 385; Joined: Fri Sep 23, 2011 9:02 pmFollowed by: 6 members; Thanked: 62 times

by user123321 » Wed Oct 19, 2011 11:27 am

if observed closely
4M = 7B
=>12M & 8B => 7(3)B&8B => 29B

if 7B takes 29 days
then 29 boys will take 7 days, which is the answer

user123321

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