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CEO
Joined: 11 Sep 2015
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Working at the same constant rate, 4 machines, working together, take
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29 Dec 2016, 12:12
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Working at the same constant rate, 4 machines, working together, take 8 days to make a total of 16 birdhouses. How many such machines are required to make 64 birdhouses in 16 days? A) 2 B) 4 C) 8 D) 16 E) 32 *Kudos for all correct solutions
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Joined: 13 Oct 2016
Posts: 367
GPA: 3.98

Re: Working at the same constant rate, 4 machines, working together, take
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29 Dec 2016, 12:48
GMATPrepNow wrote: Working at the same constant rate, 4 machines, working together, take 8 days to make a total of 16 birdhouses. How many such machines are required to make 64 birdhouses in 16 days?
A) 2 B) 4 C) 8 D) 16 E) 32
*Kudos for all correct solutions 4 machines working at a constant rate: \(\frac{1}{x} + \frac{1}{x} + \frac{1}{x} + \frac{1}{x} = \frac{16}{8}\) \(\frac{4}{x} = 2\) \(x=2\) (days per birdhouse) or just \(\frac{8}{4} = 2\) (days per birdhouse) Had the rate been kept the same we would have got 32 houses in 16 days not 64. That means we need to double the rate to fulfill this job or to double the number of machines. y  new # of machines \(\frac{y}{2} = 2*2\) \(\frac{y}{2} = 4\) \(y=8\) Answer C



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Re: Working at the same constant rate, 4 machines, working together, take
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29 Dec 2016, 18:29
Given :4 Machines  > 8 Days > 16 Bird Houses Need : ___ Machines > 16 Days > 64 BirdHouses From given 8 Machines  8 Days  32 BH => 16 M  16 D  64 BH
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CEO
Joined: 11 Sep 2015
Posts: 3438
Location: Canada

Re: Working at the same constant rate, 4 machines, working together, take
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29 Dec 2016, 19:07
GMATPrepNow wrote: Working at the same constant rate, 4 machines, working together, take 8 days to make a total of 16 birdhouses. How many such machines are required to make 64 birdhouses in 16 days?
A) 2 B) 4 C) 8 D) 16 E) 32
*Kudos for all correct solutions Another approach is to see what the original 4 machines can do in 16 days. 4 machines take 8 days to make 16 birdhouses. So, in 16 days, those same 4 machines can make 32 birdhousesSo, if we add an additional 4 machines (that can also make 32 birdhouses in 16 days), the 8 combined machines will make 64 birdhouses in 16 days. Answer: C
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Joined: 31 Oct 2013
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Concentration: Accounting, Finance
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Re: Working at the same constant rate, 4 machines, working together, take
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14 Oct 2018, 05:51
GMATPrepNow wrote: Working at the same constant rate, 4 machines, working together, take 8 days to make a total of 16 birdhouses. How many such machines are required to make 64 birdhouses in 16 days?
A) 2 B) 4 C) 8 D) 16 E) 32
*Kudos for all correct solutions Important Rule:
no. of machine *rate *Time = work.
Given,
Machine = 4
Time = 8
work = 16
we can find out the rate.
4*8*r = 16
r = 1/2.
This rate can be used to 2nd case.
machine * rate * time = work
m * 1/2 * 16 = 64
m = 8.
The best answer is C.



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Joined: 03 Mar 2017
Posts: 248

Re: Working at the same constant rate, 4 machines, working together, take
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17 Oct 2018, 10:13
4 machines, working together, take 8 days to make a total of 16 birdhouses Therefore in 4*832 machdays=6 Birdhouses 1 Bird house=2 machdays Similarly 64birdhouses=64*2 machdays Given days 16 and we need to find number of machines m Answer: m= (64*2)/16=8 mach IMO C.
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Re: Working at the same constant rate, 4 machines, working together, take
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17 Oct 2018, 10:13






