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# work

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Joined: 16 Apr 2010
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work [#permalink]  27 Jul 2010, 12:48
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100% (01:50) correct 0% (00:00) wrong based on 3 sessions
Machine A produces pencils at a constant rate of 9,000 pencils per hour, and machine B produces pencils at a constant rate of 7,000 pencils per hour. If the two machines together must produce 100,000 pencils and if each machine can operate for at most 8 hours, what is the least amount of time, in hours, that machine B must operate?

a) 4
b) 4 and 2/3
c) 5 and 1/3
d) 6
e) 6 and 1/4
[Reveal] Spoiler: OA

Last edited by Bunuel on 27 Jul 2010, 13:17, edited 1 time in total.
Edited the question.
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Re: work [#permalink]  27 Jul 2010, 13:16
Expert's post
Machine A produces pencils at a constant rate of 9,000 pencils per hour, and machine B produces pencils at a constant rate of 7,000 pencils per hour. If the two machines together must produce 100,000 pencils and if each machine can operate for at most 8 hours, what is the least amount of time, in hours, that machine B must operate?

a) 4
b) 4 and 2/3
c) 5 and 1/3
d) 6
e) 6 and 1/4

To minimize the time that machine B must operate we must maximize the time machine A can operate, so make it operate 8 hours. In 8 hours machine A will produce 8*9,000=72,000 pencils, so 100,000-72,000=28,000 pencils are left to produce, which can be produced by machine B in 28,000/7,000=4 hours.

Answer: A.

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Re: work   [#permalink] 27 Jul 2010, 13:16
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# work

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