Digging a canal

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mdavis: Senior | Next Rank: 100 Posts; Posts: 44; Joined: Thu Nov 20, 2008 2:18 pm; Thanked: 1 times

by mdavis » Tue Jan 27, 2009 7:30 pm

Could someone explain how to tackle this problem step by step? I keep missing these types of problems and don't know what I am doing wrong. Thanks!

160 men can dig 3200 m of a canal in 12 days. How many men are required to dig 3600 m more of canal in 8 days?

A) 213
B) 144
C) 270
D) 225
E) 175

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Source: Beat The GMAT — Problem Solving | Tue Jan 27, 2009 7:30 pm

Zipper: Master | Next Rank: 500 Posts; Posts: 119; Joined: Sun Nov 30, 2008 2:47 am; Thanked: 11 times

by Zipper » Tue Jan 27, 2009 8:49 pm

https://www.facebook.com/video/video.php ... 0470751740

watch this video and try for yourself

as you said you have trouble with this kinds of problem i think the video will help you learn a nice method.

g2g no time to try to solve this

btw the other videos in this group are also quite nice.

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farmanetawah: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Tue Jan 27, 2009 8:27 pm; Location: Bermuda; Thanked: 1 times

Re: Digging a canal

by farmanetawah » Tue Jan 27, 2009 9:06 pm

mdavis wrote:Could someone explain how to tackle this problem step by step? I keep missing these types of problems and don't know what I am doing wrong. Thanks!

160 men can dig 3200 m of a canal in 12 days. How many men are required to dig 3600 m more of canal in 8 days?

A) 213
B) 144
C) 270
D) 225
E) 175

so we can make it simple like this
160 men dig 3200 so
1 men dig 3200/160=20 m in 12 days
so in one day one man dig 20/12 m so
suppose x men are required to dig 3600m in one day
x=3600/ 20/12=3600*12/20=180*12 =2160
so for 8 day
2160/8=270
so c is coreect answ

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gaggleofgirls: Master | Next Rank: 500 Posts; Posts: 138; Joined: Thu Jan 15, 2009 7:52 am; Location: Steamboat Springs, CO; Thanked: 15 times

Re: Digging a canal

by gaggleofgirls » Tue Jan 27, 2009 9:39 pm

farmanetawah wrote: so we can make it simple like this
160 men dig 3200 so
1 men dig 3200/160=20 m in 12 days
so in one day one man dig 20/12 m so
suppose x men are required to dig 3600m in one day
x=3600/ 20/12=3600*12/20=180*12 =2160
so for 8 day
2160/8=270
so c is coreect answ

I like to look at it this way also because once you get the rate per person per day (or per machine per hour or per 1 worker per 1 time period) then you can take that anywhere.

With the above example you can also take a sec to reduce the fractions so the math is a bit easier.

20/12 = 5/3
rate = 5/3, we know the time = 8 days so 8*5/3 = 40/3
so 40/3 * x = 3600
x = 3600 * 3/40
x = 90 * 3 = 270

Answer = C

-Carrie

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mdavis: Senior | Next Rank: 100 Posts; Posts: 44; Joined: Thu Nov 20, 2008 2:18 pm; Thanked: 1 times

by mdavis » Wed Jan 28, 2009 7:56 am

Thanks so much for the help!

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