Work Problem

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sarahw_gmat: Junior | Next Rank: 30 Posts; Posts: 26; Joined: Fri Mar 12, 2010 1:39 pm; Thanked: 1 times

by sarahw_gmat » Wed May 05, 2010 12:50 pm

How to solve below problem?

If 7 workers can build 7 cars in 7 days, then how many days would it take 5 workers to build 5 cars?

Thanks.

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Source: Beat The GMAT — Quantitative Reasoning | Wed May 05, 2010 12:50 pm

sk818020: Master | Next Rank: 500 Posts; Posts: 214; Joined: Mon Mar 29, 2010 1:46 pm; Location: Houston, TX; Thanked: 37 times; GMAT Score:700

by sk818020 » Wed May 05, 2010 3:29 pm

Assuming they are all working at the same rate, then 7 workers working for 7 days build cars 7 means that each worker is building 1/7 of a car a day. 5 workers working at 1/7 car a day means that they work together a 5/7 cars per day. To build 5 cars it would take;

rate * time = work

rt = w

(5/7)t= 5

t=5/(5/7)= (5/1)(7/5)=7

So it takes 5 workers 7 days to build 5 cars. Again, assuming no worker is working more efficient or less efficient than any other.

Hope that helps.

Thanks,

Jared

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sarahw_gmat: Junior | Next Rank: 30 Posts; Posts: 26; Joined: Fri Mar 12, 2010 1:39 pm; Thanked: 1 times

by sarahw_gmat » Thu May 06, 2010 2:21 pm

Wasn't sure how to calculate work per person per day. Now it makes sense.
Thanks.

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harshavardhanc: Legendary Member; Posts: 526; Joined: Sat Feb 21, 2009 11:47 pm; Location: India; Thanked: 68 times; GMAT Score:680

by harshavardhanc » Fri May 07, 2010 12:28 am

sarahw_gmat wrote:How to solve below problem?

If 7 workers can build 7 cars in 7 days, then how many days would it take 5 workers to build 5 cars?

Thanks.

another way to solve this kind of problem :

think in terms of proportionality.

number of people remaining same, more work will be done if you increase the number of days they work.

Therefore, days ~ work .

similarly, if the number of days is constant, more work will be done if you increase the number of ppl working on it.

hence, number of ppl ~ work.

So, you can convert this into an equation which will be number * days = work OR n * d = w.

once you get this equation, just use (n1 * d1) / (n2* d2) = w1/ w2

for the case in hand, (7 *7)/(5 * x) = 7/5 => x = 7

quite mechanical! isn't it?

Regards,
Harsha

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hephzi_bah: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Thu Apr 10, 2008 6:23 am; GMAT Score:800

by hephzi_bah » Mon May 10, 2010 12:52 pm

sarahw_gmat wrote:Wasn't sure how to calculate work per person per day. Now it makes sense.
Thanks.

I prefer to use my way:

Sincerely
Alberto Vidal

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sumanr84: Legendary Member; Posts: 758; Joined: Sat Aug 29, 2009 9:32 pmFollowed by: 2 members; Location: Bangalore,India; Thanked: 67 times

by sumanr84 » Wed Jun 16, 2010 8:24 pm

hephzi_bah wrote:
sarahw_gmat wrote:Wasn't sure how to calculate work per person per day. Now it makes sense.
Thanks.
I prefer to use my way:

Sincerely
Alberto Vidal

Alberto,
I am curious to know your strategy for this problem. Could you elaborate a little on this ? What is the limitation,if any, of this approach ?

I am on a break !!

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