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A copy machine, working at a constant rate, makes 35 copies

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A copy machine, working at a constant rate, makes 35 copies [#permalink] New post 25 Jun 2012, 08:32
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A copy machine, working at a constant rate, makes 35 copies per minute. A second copy machine, working at a constant rate, makes 55 copies per minute. Working together at their respective rates, how many copies do the two machines make in half an hour ?

A. 90
B. 2,700
C. 4,500
D. 5,400
E. 324,000
[Reveal] Spoiler: OA
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Re: A copy machine, working at a constant rate, makes 35 copies [#permalink] New post 25 Jun 2012, 08:48
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A copy machine, working at a constant rate, makes 35 copies per minute. A second copy machine, working at a constant rate, makes 55 copies per minute. Working together at their respective rates, how many copies do the two machines make in half an hour ?

A. 90
B. 2,700
C. 4,500
D. 5,400
E. 324,000

Together the two machines make 35+55=90 copies per minute. So, in half an hour they will make 90*30=2,700 copies.

Answer: B.
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Re: A copy machine, working at a constant rate, makes 35 copies [#permalink] New post 14 Nov 2012, 23:59
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Rate1+Rate2=CombinedRate
\frac{35}{1min}+\frac{55}{1min}=\frac{90}{1min}
\frac{90}{1min}(30min)=2,700copies

Answer:B
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Re: A copy machine, working at a constant rate, makes 35 copies [#permalink] New post 29 Apr 2013, 23:01
why not 1/35 + 1/55 = 18/385 for 2 copies?
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Re: A copy machine, working at a constant rate, makes 35 copies [#permalink] New post 29 Apr 2013, 23:50
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shahebali wrote:
why not 1/35 + 1/55 = 18/385 for 2 copies?


1/35 minutes is the time the first machine needs to make one copy.
1/55 minutes is the time the second machine needs to make one copy.

Why are you adding them?
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Re: A copy machine, working at a constant rate, makes 35 copies [#permalink] New post 07 May 2013, 15:09
darn did something stupid
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Re: A copy machine, working at a constant rate, makes 35 copies [#permalink] New post 05 Jun 2013, 15:37
Machine A = 35 copies per minute. 35*30 = 1050 copies in 30 minutes
Machine B = 55 copies per minute. 55*30 = 1650 copies in 30 minutes
1050+1650 = 2700 copies in 30 mins
Re: A copy machine, working at a constant rate, makes 35 copies   [#permalink] 05 Jun 2013, 15:37
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