Rate problem anyone?

[eclaym2003]

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!!!!

[raleigh]

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.

[eclaym2003]

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.

[eclaym2003]

Would this be considered a 700-800 pt question? Just curious...

[abhinav85]

I don't think so that its a 700-800 ques,
its more or like 500-600 level.

[eclaym2003]

Would this be considered a 700-800 pt question? Just curious...

[raleigh]

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.