It would take one machine 4 hours to complete a large produc

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It would take one machine 4 hours to complete a large produc [#permalink]

17 Dec 2012, 06:29

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69% (01:45) correct

30% (00:47) wrong

based on 9 sessions

It would take one machine 4 hours to complete a large production order and another machine 3 hours to complete the same order. How many hours would it take both machines, working simultaneously at their respective constant rates, to complete the order?

(A) 7/12
(B) 1 1/2
(C) 1 5/7
(D) 3 1/2
(E) 7

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Re: It would take one machine 4 hours to complete a large produc [#permalink]

17 Dec 2012, 06:33

Walkabout wrote:

The rate of the first machine is 1/4 job per hour;
The rate of the second machine is 1/3 job per hour;

Thus, the combined rate of the machines is 1/4+1/3=7/12 job per hour, which means that it takes 1/(7/12)=12/7 hours both machines to do the job.

Answer: C.
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Re: It would take one machine 4 hours to complete a large produc [#permalink] 17 Dec 2012, 06:33

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It would take one machine 4 hours to complete a large produc

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It would take one machine 4 hours to complete a large produc

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