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4th Ed-SG# 4, Chapter 3, Problem 14

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soaringAlone
 Post subject: 4th Ed-SG# 4, Chapter 3, Problem 14
 Post Posted: Sat Aug 06, 2011 9:46 am 
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Students


Posts: 8
Can someone explain how did we arrive at 107 minutes if partial loading were allowed ?
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mithunsam
 Post subject: Re: 4th Ed-SG# 4, Chapter 3, Problem 14
 Post Posted: Tue Aug 09, 2011 9:57 pm 
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Course Students


Posts: 76
Assuming that you understand how we arrive at 80 mins & 64 mins for the two machines...

Machine A takes 80 mins for 1 unit of work
Machine B takes 64 mins for 1 unit of work

How much time would the machines together take for 1 unit of work?

1/80 + 1/64 = 1/h
9/320 = 1/h
320/9 = h

How much time would the machines together take for 3 units of work?

h = (320/9) * 3
h = 320/3 ~ 107 mins
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mithunsam
 Post subject: Re: 4th Ed-SG# 4, Chapter 3, Problem 14
 Post Posted: Tue Aug 09, 2011 10:05 pm 
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Course Students


Posts: 76
One more point...

Book says to divide the load between the machines as 4/9 and 5/9 respectively. However, we can avoid this computation.

We just have to remember that when two machines work together, the fastest they could finish a job is when none of the machines sit idle. That means, both the machines have to work for the same amount of time. In other words, the fastest completion time will depend on the average rate of the machines together. That is all I have done above.
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tim
 Post subject: Re: 4th Ed-SG# 4, Chapter 3, Problem 14
 Post Posted: Fri Aug 12, 2011 11:28 pm 
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ManhattanGMAT Staff


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Location: Southwest Airlines, seat 21C
thanks..

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Tim Sanders
Manhattan GMAT Instructor
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soaringAlone
 Post subject: Re: 4th Ed-SG# 4, Chapter 3, Problem 14
 Post Posted: Wed Mar 14, 2012 1:38 am 
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Students


Posts: 8
Thanks mithunsam, You have explained it from a different angle and I get it now.

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~soaringAlone
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tim
 Post subject: Re: 4th Ed-SG# 4, Chapter 3, Problem 14
 Post Posted: Sun Mar 18, 2012 1:40 am 
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ManhattanGMAT Staff


Posts: 2183
Location: Southwest Airlines, seat 21C
glad to hear it!

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Tim Sanders
Manhattan GMAT Instructor
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