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# Each of 10 machines works at the same constant rate doing a

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Intern
Joined: 10 Jan 2005
Posts: 4
Location: Toronto
Each of 10 machines works at the same constant rate doing a [#permalink]

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12 Nov 2008, 19:30
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Each of 10 machines works at the same constant rate doing a certain job. The amount of time 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?

1)18
2)20
3)22
4)24
5)26
Director
Joined: 14 Aug 2007
Posts: 704
Re: 1 question from PPrep [#permalink]

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12 Nov 2008, 19:42
sessmi wrote:
Each of 10 machines works at the same constant rate doing a certain job. The amount of time 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?

1)18
2)20
3)22
4)24
5)26

B.20

1 = (Rate of 10 machines) * 16 hrs
Rate of 10 machines = 1/16 wk/hr
each machine works at constant speed , so
Rate of 1 machine = 1/160 wk/hr

when there are 8 machines

8*1/160* time = 1 wk
time = 20 hrs
Intern
Joined: 10 Jan 2005
Posts: 4
Location: Toronto
Re: 1 question from PPrep [#permalink]

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12 Nov 2008, 19:54
got it.

thanks very much alpha_plus_gamma!!
Re: 1 question from PPrep   [#permalink] 12 Nov 2008, 19:54
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# Each of 10 machines works at the same constant rate doing a

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