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Work rate combination problem

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by sethn23 » Wed Oct 01, 2008 6:15 pm
Each of 10 machines works at a constant rate. When working together the amount of time it takes to complete a job is 16 hrs. How many hours will it take to complete the same job if only 8 machines work together?

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Re: Work rate combination problem

by Morgoth » Wed Oct 01, 2008 6:34 pm
sethn23 wrote:Each of 10 machines works at a constant rate. When working together the amount of time it takes to complete a job is 16 hrs. How many hours will it take to complete the same job if only 8 machines work together?

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rate * time * no. of machines = work

rate * 16 * 10 = 1

rate = 1/160

rate * time * no. of machines = work

1/160*time*8= 1

time = 160/8 = 20.

Hope this helps.
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by sethn23 » Wed Oct 01, 2008 6:38 pm
thanks again Morgoth
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by allechat » Thu Oct 02, 2008 12:38 pm
could you also look at this as, # of machines is reduced by 1/5, so it's going to take 1/5 more time?

20 is 1/5 more time than 16.

change formula: (10-8)/10 machines= 1/5 fewer machines

then (x-16)/x=1/5, 5x-80=x
5x=x+80, x=20
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Very simple formula

by peddisetty » Sun Feb 15, 2009 3:39 pm
You can use M1D1W2 = M2D2W1.

So, here its M1D1 = M2D2 => 10*16 = 8*x

x = 20.

Very simple........
Raj Peddisetty
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by sureshbala » Tue Feb 17, 2009 7:59 pm
Since 10 machines take 16 hrs, it is clear that the work takes 160 machine hours. Since now we have 8 machines, to contribute those 160 machine hours, time taken is 160/8 = 20.

The same thing is explained above in the form of a forumula
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Re: Work rate combination problem

by griscomtestprep » Wed Feb 18, 2009 12:23 am
sethn23 wrote:Each of 10 machines works at a constant rate. When working together the amount of time it takes to complete a job is 16 hrs. How many hours will it take to complete the same job if only 8 machines work together?

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Since there are 8/10 of the machines, it is going to take 10/8 as long.
10/8 * 16 = 20
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by missrochelle » Wed Aug 25, 2010 9:07 pm
sethn23 wrote:Each of 10 machines works at a constant rate. When working together the amount of time it takes to complete a job is 16 hrs. How many hours will it take to complete the same job if only 8 machines work together?

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What are you supposed to recognize in this problem that states the total time is 160hrs? I assumed each machine worked 1/16 hr which is wrong...
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