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dferm
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 Posted: Mon Mar 24, 2008 1:38 pm Post subject: GMAT PREP???? |
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A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hours and a machine of type S does the same job in 18 hours. If the company used the same number of each type of machine to do the job in 2 hours, how many machines of type R were used?
A. 3
B. 4
C. 6
D. 9
E. 12 |
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xilef
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| Posted: Mon Mar 24, 2008 1:58 pm Post subject: |
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using work formula to find the time it takes for both machines to do the same work:
(18*36)/54=12 hrs for both machines to complete the job
2 hrs is 6 times faster so the company needs 6 of each to do it in 12hr.
Answer C. |
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preciousrain7
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| Posted: Mon Mar 24, 2008 2:47 pm Post subject: |
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| xilef wrote: | using work formula to find the time it takes for both machines to do the same work:
(18*36)/54=12 hrs for both machines to complete the job
2 hrs is 6 times faster so the company needs 6 of each to do it in 12hr.
Answer C. |
Can you give more explanation for the last step please? Thanks! |
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xilef
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| Posted: Mon Mar 24, 2008 3:04 pm Post subject: |
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| It takes both working together (one of each machine) to do the job in 12hrs. The company used the same number of each type of machine to do the job in 2 hours, which is 6 times faster than the the time it takes one of each machine to do the job, therefore, company used 6 of each. |
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preciousrain7
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Thanked 2 times in 2 posts
Location: NYC, NY
Test Date: Jan 25th
Target GMAT Score: 700
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| Posted: Mon Mar 24, 2008 3:31 pm Post subject: |
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| xilef wrote: | | It takes both working together (one of each machine) to do the job in 12hrs. The company used the same number of each type of machine to do the job in 2 hours, which is 6 times faster than the the time it takes one of each machine to do the job, therefore, company used 6 of each. |
thanks! |
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