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# work

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work [#permalink]  25 Jan 2009, 11:10
6 machines take 12 days to complete a job. How many more machines will be needed to complete the job in 8 days?

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Re: work [#permalink]  25 Jan 2009, 11:19
The job requires 6*12 = 72 total days of machine work. So, one machine would do the job in 72 days, two machines in 36 days, three machines would need 24 days, etc. To do the job in 8 days, we'd need 9 machines in total, or 3 additional machines.
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Last edited by IanStewart on 25 Jan 2009, 14:56, edited 1 time in total.
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Re: work [#permalink]  25 Jan 2009, 12:22
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If 6 machines take 12 days to complete the task, one machine takes 72 days. Let X be number of machines and d the number of days:
$$\frac{x}{72}=\frac{1}{d}$$

What you want is for d to equal 8, so X must be nine and you'll need 3 more machines.
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Re: work [#permalink]  27 Jan 2009, 09:39
6 machines take 12 days to complete a job. How many more machines will be needed to complete the job in 8 days?

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This question is on inverse proportions.
Its btw number of machines and days.

so md = k ( constant)

6x12 = m x 8

6 x 12 / 8 = m

9 = m

how many more = 9 - 6 = 3

Re: work   [#permalink] 27 Jan 2009, 09:39
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