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Six machines, each working at the same constant rate [#permalink]
05 Feb 2012, 22:28

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72% (01:41) correct
28% (00:33) wrong based on 381 sessions

Six machines, each working at the same constant rate, together can complete a job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?

Re: Help! GMATPrep question [#permalink]
06 Feb 2012, 01:04

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Welcome to GMAT Club. Below is a solution for the question. Hope it helps

Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days? A. 2 B. 3 C. 4 D. 6 E. 8

Let x be the time needed for 1 machine to complete the job, so rate of one machine is \frac{1}{x} (rate is the reciprocal of time) --> rate of 6 machines would be \frac{6}{x}.

As job=time*rate --> 1=12*\frac{6}{x} --> x=72 days needed for 1 machine to complete the job.

To complete the job in 8 days \frac{72}{8}=9 machines are needed.

Six machines, each working at the same constant rate, together c [#permalink]
30 Apr 2013, 22:27

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njss750 wrote:

6 machines each working @ the same constant rate together can complete a certain job in 12 days. How many additional machines are reqd (each working at same constant rate) to finish the job in 8 days? 2 3 4 6 8

Pl xplain with wkgs

6 x 12 = (6+x) x 8

9 = 6+x

x=3 _________________

Kabilan.K Kudos is a boost to participate actively and contribute more to the forum

Re: Six machines, each working at the same constant rate [#permalink]
12 Aug 2013, 10:52

srkaleem wrote:

Six machines, each working at the same constant rate, together can complete a job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?

A. 2 B. 3 C. 4 D. 6 E. 8

Somehow, I found below method to be working for me - 6 Machines in 12 Days do 1 Work i.e. in notation form 6M * 12D = 1W, so 1M * 1D = [1/(6*12)] W How many Machines in 8 Days will complete 1 Work? i.e. xM * 8D = [(x*8)/(6*12)] W = 1W

Solving for x in [(x*8)/(6*12)] = 1, we get x = 9 i.e. 9 Machines in 8 Days will do 1 Work. So 9-6=3 Machines more are required.

Re: Six machines, each working at the same constant rate [#permalink]
12 Aug 2013, 11:50

srkaleem wrote:

Six machines, each working at the same constant rate, together can complete a job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?