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Rate problem anyone?

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Rate problem anyone?

by eclaym2003 » Fri May 29, 2009 7:24 pm
OK so I have the GMAT tomorrow afternoon but there is one more problem that I cannot let go. It is this weird rate problem.

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 must produce 100,000 pencils and each machine can operate at most 8 hours, what is the least amount of time, in hours, that machine B must operate?

1.)4
2.)4 2/3
3.)5 1/3
4.)6
5.)6 1/4

I am pretty proficient at rate problems but I spent so much time on this one and I was pretty sure I solved it correctly, only to find out that I missed it. ARGGG!!!!
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by raleigh » Fri May 29, 2009 7:45 pm
The question asks for the least amount of time that machine B would have to run. It does not ask how long does it take the two machines working together.

For machine B to run the least, machine A should run as long as possible, 8 hours. In those 8 hours, it makes 9000(pencils/hour)*8(hours) = 72,000 pencils.

So machine B must make 100,000 - 72,000 = 28,000 pencils.

28,000(pencils)/7,000(pencils/hour) = 4 hours.

The answer is 1.

Did you do this as a standard work problem? If machine A and B ran together, it would take them 6 hours to make 100,000 pencils.
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by eclaym2003 » Sat May 30, 2009 6:21 am
Yeah, I did this as a standard rate problem. I think that's why I was so confident that I solved it correctly. Thanks for the help. I actually got this problem during the GMAT prep software CAT.
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by eclaym2003 » Sat May 30, 2009 6:33 am
Would this be considered a 700-800 pt question? Just curious...
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by abhinav85 » Sat May 30, 2009 6:49 am
I don't think so that its a 700-800 ques,
its more or like 500-600 level.
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by eclaym2003 » Sat May 30, 2009 7:28 am
Would this be considered a 700-800 pt question? Just curious...
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by raleigh » Sat May 30, 2009 11:07 am
The hard part of this problem is completely reading it so you understand what you are asked for.

I find this is my biggest problem in my preparation right now. GMAC knows that you can be very good with work problems, so they'll ask for something that isn't typical.
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