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Work and time problem.please help

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by boros2203 » Tue Sep 07, 2010 11:05 am
Machine A, working alone at its constant rate, manufactures 280 bolts per hour, and machine B, working alone at its constant rate, manufactures 220 bolts per hour. How many hours will it take for machines A and B, working together at their respective constant rates, to manufacture 1,000 bolts?

(A) 1
(B) 1.3
(C) 1.5
(D) 1.8
(E) 2

Hi I have a doubt with this question. OA given is E but i am not convinced by it. With E as answer it is suggesting that A and B worked independently for 2hrs each.

Please let me know whether I have interpreted the question wrongly ....[/spoiler]
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by crazy_genius » Tue Sep 07, 2010 11:29 am
Boros,

Working 'together' implies working simultaneously (though independently). when the question says that Mac. A and B work 'together', it means that these machines do not work at different timings and they do not stop in between. Therefore, they will ultimately work 'on their own' or 'independently' ( as used by you), yet they work 'together'

Hence the answer (E) 2 is correct.
~A.K~

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by sdotcruz » Tue Sep 07, 2010 11:31 am
E is correct and you are correct that it is like they are working alone for 2 hours. The combined rate would be 500 bolts per hour because after an hour of running the machines you will find one produced 220 bolts and the other 280 bolts. When you were given rates your can combine the rates as R(total) = R(1) +R(2). THis problem seems very straight forward. You may find other instances where you are given the time to complete a job. When you find that type of problem you will need a different formula and the solution will be longer.
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by boros2203 » Tue Sep 07, 2010 11:39 am
Thanks everyone ....
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by Scott@TargetTestPrep » Sat Jul 07, 2018 5:29 pm
boros2203 wrote:Machine A, working alone at its constant rate, manufactures 280 bolts per hour, and machine B, working alone at its constant rate, manufactures 220 bolts per hour. How many hours will it take for machines A and B, working together at their respective constant rates, to manufacture 1,000 bolts?

(A) 1
(B) 1.3
(C) 1.5
(D) 1.8
(E) 2
Since the combined rate is 500 bolts per hour, then it will take 1,000/500 = 2 hours for the two machines to manufacture 1,000 bolts.

Answer: E

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