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Six machines, each working at the same constant rate [#permalink]
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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: Six machines, each working at the same constant rate [#permalink]
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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 [#permalink]
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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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GMAT PREP (PS) [#permalink]
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27 Apr 2010, 09:49
Please explain the quick and logical approach
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Re: GMAT PREP (PS) [#permalink]
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27 Apr 2010, 12:13



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Re: GMAT PREP (PS) [#permalink]
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27 Apr 2010, 14:39
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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Re: Six machines, each working at the same constant rate [#permalink]
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19 Jun 2010, 19:52
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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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Re: GMAT PREP (PS) [#permalink]
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16 Jun 2011, 13:56
6*12/1= (6+X)8
X=3



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Re: GMAT PREP (PS) [#permalink]
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18 Jun 2011, 18:56
Lets look at this way :As the rate of one machine is constant i e 1/(12*6)=1/72 .Even after addition of extra machines the rate will remain the same .Hence,if machines are x now ,the rate becomes 1/8x which is equal to 1/72. X comes out to be 9 . Machines added=96=3
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Re: GMAT PREP (PS) [#permalink]
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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: GMAT PREP (PS) [#permalink]
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05 Aug 2011, 09:02
6 machines  1 unit of work  12 days
=> 1 machine = 1/72 of work per day
=> rate of each machine = 1/72
equating work done by 6 machines and 6+x machines
1 = (1/72)(6+x)(8)
=> x = 3
Answer is B.



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Re: GMAT PREP (PS) [#permalink]
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05 Aug 2011, 13:17
6 machines 12 days... therefore (6*12)/8=9number of machines required to complete the job in 8 days Therefore additional machines required=96=3 Answer is B
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Re: GMAT PREP (PS) [#permalink]
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30 Sep 2011, 20:44
Hi, can someone tell me if this is really a level 700 question? I felt like this was so much easier than some of the other questions posted but its labelled as level 700.



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Re: GMAT PREP (PS) [#permalink]
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30 Sep 2011, 23:22
musicbelle wrote: Hi, can someone tell me if this is really a level 700 question? I felt like this was so much easier than some of the other questions posted but its labelled as level 700. Yes its definitely not a 700 level question but then rating of a question on a forum is as per the poster. A 700 level question for me can look like a 500 for you and viceversa. I would rather concentrate on the take aways from each question



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Re: GMAT PREP (PS) [#permalink]
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06 Jan 2012, 06:28
Nice question. Nice solutions by many. Thanks all. Easy one. 3 more machines are required.
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Re: GMAT PREP (PS) [#permalink]
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06 Jan 2012, 20:53
This is effectively an inverse proportionality problem. 6M > 12 days > 1 work X > 8 days > 1 work X x 8 = 6 x 12 X = 9 Therefore, additional machines = 96 = 3
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Re: Six machines, each working at the same constant rate [#permalink]
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04 Mar 2013, 00:09
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 6 * rate * 12 = # of Machine * rate * 8. # of machine =( 6 *12) / 8 = 9. 9  6 = 3 additional machines required
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