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# Work rate problem - Gmat prep

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Intern
Joined: 01 Nov 2006
Posts: 19
Work rate problem - Gmat prep [#permalink]

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16 Dec 2006, 14:30
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Can someone help with this problem?

Each of 10 machines works at the same constant rate doing a certain job. The amount needed by the 10 machines working together, to complete the job is 16 hours. How many hours would be needed if only 8 of the machines, working together were used to complete the job?
Director
Joined: 26 Feb 2006
Posts: 899
Re: Work rate problem - Gmat prep [#permalink]

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16 Dec 2006, 15:30
sassymar111 wrote:
Can someone help with this problem?

Each of 10 machines works at the same constant rate doing a certain job. The amount needed by the 10 machines working together, to complete the job is 16 hours. How many hours would be needed if only 8 of the machines, working together were used to complete the job?

if nothing is hidden assumption:

= (10 x 16) / 8 = 20
Senior Manager
Joined: 20 Feb 2006
Posts: 373

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16 Dec 2006, 16:47
Work done = Rate * Time

Let x = rate of machine

So: 10*(1/x) = 1/16

10/x = 1/16 -------> 160 = x

Now time for one machine doing the job = 160hrs

For 8 machines, y = total time:

8*(1/160) = 1/y

8/160 = 1/y --------> 8y = 160 -----> y = 20

Time needed = 20 hours
Intern
Joined: 07 Aug 2006
Posts: 8

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14 Jan 2007, 07:28
If you want more help with this type of question then you will find this rate problems tutorial and practice question set very helpful.
14 Jan 2007, 07:28
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# Work rate problem - Gmat prep

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