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Machine A produces pencils at a constant rate of 9000 [#permalink]
24 Mar 2006, 18:59

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Difficulty:

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Question Stats:

0% (00:00) correct
0% (00:00) wrong based on 0 sessions

Machine A produces pencils at a constant rate of 9000 pencils per hour, and machine B produces pencils at a constant rate of 7000 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 2/3
C-5 1/3
D-6
E-6 1/4

This is how I solved it. Can you tell me if it is wrong or not?

Maximum hours machines can operate is 8.

So I said 8 * 9000 = 72000
That is 28000 short of 100,000
so 28000/7000 = 4 and hence Machine B only needs to operate 4 hours.

Is this the right way? The answer is 4 but I want to make sure I'm not just getting the right answer by luck.