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Six machines, each working at the same constant rate
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26 Apr 2010, 21:53
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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
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Re: Help! GMATPrep question
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06 Feb 2012, 02:04
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. Difference: 96=3. Answer: B.
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Re: Help! GMATPrep question
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05 Feb 2012, 23:54
6 machines in 12 hours can make 6*12=72 units. x machines in 8 hours can make x*8=72 units x=9 129=3 more machines are needed hope it helps
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Re: Six machines, each working at the same constant rate
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26 Apr 2010, 22:50
zz0vlb wrote: 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 Source: GMAT Prep let each machine work at rate of x days 1/x+1/x+1/x+1/x+1/x+1/x = 1/12 6/x = 1/12 x = 72 now y is number of machines needed to complete job in 8 days so, y/72 = 1/8 y = 9 required = yx = 3 hence b.



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Re: Six machines, each working at the same constant rate
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27 Apr 2010, 06:02
zz0vlb wrote: 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 Source: GMAT Prep Another solution which is faster is Since each machine works at a constant rate. The time needs to bought down from 12 to 8. So the new time is 2/3 of the original time. Thus to achieve this we need the rate to be 3/2 of original. So 3/2* 6 = 9 So we need 96 = 3 more machines.
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Six machines, each working at the same constant rate
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27 Apr 2010, 12:13



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Re: Six machines, each working at the same constant rate
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19 Jun 2010, 19:52
Actually, this was more simple than I thought. When I first saw this, I started to panic thinking it's a rate question. But then I took a step back, and it was the simplest of calculations.
So here's the deal:
12 days > 6 machines: 8 days > ?
8 days means you definitely need more machines than the 6 and in such case the equation looks like
12 * 6 = 8 * x
Therefore, x = 72 / 8 = 9
So 96=3 more machines



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05 Aug 2011, 04:50
6 machines require 12 days = 72 machine days how many machines to do the job in 8 days = \(\frac{72 machinedays}{8 days} = 9 machines\)
so, 3 more machines.
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Re: Six machines, each working at the same constant rate
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06 Feb 2012, 06:58
6*12 = 72 units > 72Units / 8hours = X > X = 9
Answer B



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Re: Six machines, each working at the same constant rate
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03 May 2012, 09:47
This is how I did it
6 machines in 1hr do 1/12 job in 1 hr, 1 machine do 1/(12*6) job In 8 days 1 machine do 8/(12*6)=1/9
Thus there is a need of 9 machine.
But I forgot to minus and get the difference so still get this question wrong.



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Re: Six machines, each working at the same constant rate
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14 Nov 2012, 00:32
\(Rate of machine = \frac{1}{m}\) Draw the equation for 6 machines take 12 days: \(\frac{6}{m}=\frac{1}{12}\) \(m=72 days\) Let's look for the number of machines to work for 8 days: \(\frac{N}{72}=\frac{1}{8}\) \(N=\frac{72}{8}=9 machines\) Answer: 9  6 machines = 3 machines more B
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Six machines, each working at the same constant rate, together c
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30 Apr 2013, 23:27
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
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Re: 6 machines each working @ the same constant rate together
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01 May 2013, 01:06
You can solve this problem without any equations. Just to calculate the rate of 1 machine. The rate of 1 machine is \(\frac{1}{6*12}=\frac{1}{72}\) part per day. So, 1 machine in 8 days can do \(\frac{8}{72}=\frac{1}{9}\). So, to finish the job in 8 days we need 9 machines. Therefore 3 additional machines are required. The answer is B.
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Re: Six machines, each working at the same constant rate
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12 Aug 2013, 11:52
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 96=3 Machines more are required. Ans  B



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Re: Six machines, each working at the same constant rate
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12 Aug 2013, 12:50
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?
A. 2 B. 3 C. 4 D. 6 E. 8 Here, 6 × 1/X = 1/12 or, X=72 . 2nd case, n × 1/72 = 1/8 or, n = 9 . additional = 96 = 3
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Re: Six machines, each working at the same constant rate
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25 Aug 2014, 05:37
since machine and work in inversely related. thus it is inverse proportion
6 x 12 = 8 x N (let n be the number of person required.)
N=9
thus the number of additional person is 96 = 3



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Re: Six machines, each working at the same constant rate
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26 Aug 2014, 01:57
6 Machines do \(\frac{1}{12}\) work in 1 day We require \(\frac{1}{8}\) work to be done in 1 day Multiplication factor\(= \frac{\frac{1}{8}}{\frac{1}{12}} = \frac{1}{8} * 12 = \frac{3}{2}\) Additional machines required \(= 6 * \frac{3}{2}  6 = 9  6 = 3\) Answer = B
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Re: Six machines, each working at the same constant rate
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26 Dec 2014, 15:00
Six Machines:combined rate=6x Time=12 Let Job be J
6x*12=J
Let M be the number of machines required to complete job in 8 days Then Mx*8=J
6x*12=Mx*8
M=9
Additional=96=3
Is this approach correct??



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Re: Six machines, each working at the same constant rate
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07 Apr 2018, 10:40
Hi All, We're told that 6 machines, working at the same constant rate, can finish a job in 12 days. We're asked for the number of EXTRA machines will you need to finish the job in 8 days? This type of question is easiest to solve if you convert the info into "work units" Here, we start with 6 machines working for 12 days. This equals (6)(12) = 72 machinedays of work to finish the job. If we wanted to finish the job in 8 days, it would still take 72 machinedays of work, so we'd need 72/8 = 9 machines. We already have 6 machines, so we need 3 MORE machines to get the job done in 8 days. Final Answer: GMAT assassins aren't born, they're made, Rich
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Re: Six machines, each working at the same constant rate
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25 Jun 2018, 12:12
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 We are given that six machines, each working at the same constant rate, together can complete a certain job in 12 days. Since rate = work/time and if we consider work as 1, the rate of the six machines is 1/12. We need to determine how many additional machines, each working at the same constant rate, will be needed to complete the same job in 8 days. In other words we need to determine how many additional machines are needed to work at a rate of 1/8. Since each machine works at the same constant rate, we can use a proportion to first determine the number of machines needed to work at the rate of 1/8. Our proportion is as follows: 6 machines is to a rate of 1/12 as x machines is to a rate of 1/8. 6/(1/12) = x/(1/8) 72 = 8x x = 9 So we need 9 – 6 = 3 more machines. Answer: B
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