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A company has two types of machines, type R and type S

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A company has two types of machines, type R and type S [#permalink] New post 02 Apr 2012, 12:55
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Question Stats:

72% (01:59) correct 28% (01:00) wrong based on 238 sessions
A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hrs and a machine of type S does the same job in 18 hours. If the company used the same number of each type of machine to do the job in 2 hours, how many machines of type R were used?

A. 3
B. 4
C. 6
D. 9
E. 12
[Reveal] Spoiler: OA

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Re: Two machines [#permalink] New post 02 Apr 2012, 16:58
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enigma123 wrote:
A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hrs and a machine of type S does the same job in 8 hours. If the company used the same number of each type of machine to do the job in 2 hours, how many machines of type R were used?

A. 3
B. 4
C. 6
D. 9
E. 12


Rate of A - \frac{1}{36} job/hour, rate of x machines of A - \frac{1}{36}x job/hour;
Rate of B - \frac{1}{18} job/hour, rate of x machines of B - \frac{1}{18}x job/hour, (same number of each type);

Remember that we can sum the rates, hence combined rate of A and B is \frac{1}{36}x+\frac{1}{18}x=\frac{3}{36}x=\frac{1}{12}x job/hour.

We are told that together equal number (x in our case) of machines A and B can do the job (1 job) in 2 hours --> Time*Rate=2*\frac{1}{12}x=1=Job --> x=6.

Answer: C.
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Re: A company has two types of machines, type R and type S [#permalink] New post 03 Apr 2012, 02:56
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After tearing my hair apart for 30 mins, saw Bunuels solution and realized the question is wrong. Its 18 not 8
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Re: A company has two types of machines, type R and type S [#permalink] New post 03 Apr 2012, 05:49
enigma123 wrote:
A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hrs and a machine of type S does the same job in 18 hours. If the company used the same number of each type of machine to do the job in 2 hours, how many machines of type R were used?

A. 3
B. 4
C. 6
D. 9
E. 12


Take total work as 360

R:
work : 360
time: 36hrs
rate: 10(calculaed)

S:
Work:360
time 18hrs
rate: 20( calculated)

together

given work:360
time2 hrs
calculated: 180
rate: 180/(10+20) = 180/30 = 6 each
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A company has two types of machines, type R and type S [#permalink] New post 15 Aug 2012, 10:16
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above720 wrote:
Here is a work problem from GMATPrep, Practice Test 1:

A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hours and a machine of type S does the same in job in 18 hours. If the company used the same number of each type of machine to do the job in 2 hours, how many machines of type R were used?

a) 3
b) 4
c) 6
d) 9
e) 12


Machine R does a job in 36 Hours. Machine S in 18 Hours.
Together, the machines R & S can finish the job in \frac{(36*18)}{(36+18)}= 12 Hours
In other words,
1 machine of R + 1 machine of S can finish the job together in = 12 Hours

So, to finish the job in 2 Hours, company needs 6 machines of each type - Option C
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Re: A company has two types of machines, type R and type S [#permalink] New post 15 Nov 2012, 04:53
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Let N be the number of machines...
\frac{N}{36}+\frac{N}{18}(2hours)=1
\frac{3N}{18}=1==>N=6

ANswer: 6 machines
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Re: A company has two types of machines, type R and type S [#permalink] New post 25 Feb 2013, 02:36
So the number of macines in this question is just the time in this particular question?
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Re: A company has two types of machines, type R and type S [#permalink] New post 25 Feb 2013, 13:29
I am not sure I understand your question correctly. The number of machines is not equal to the time. Instead, the number of machines has to be replied with the time taken by each machine to get the total time required to complete the job.

Hope this helps but in case it doesn't, could you please state your question more elaborately?

fozzzy wrote:
So the number of macines in this question is just the time in this particular question?

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Re: A company has two types of machines, type R and type S [#permalink] New post 04 Mar 2013, 02:45
arnabghosh wrote:
above720 wrote:
Here is a work problem from GMATPrep, Practice Test 1:

A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hours and a machine of type S does the same in job in 18 hours. If the company used the same number of each type of machine to do the job in 2 hours, how many machines of type R were used?

a) 3
b) 4
c) 6
d) 9
e) 12


Machine R does a job in 36 Hours. Machine S in 18 Hours.
Together, the machines R & S can finish the job in \frac{(36*18)}{(36+18)}= 12 Hours
In other words,
1 machine of R + 1 machine of S can finish the job together in = 12 Hours

So, to finish the job in 2 Hours, company needs 6 machines of each type - Option C


Used the same method.
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Re: A company has two types of machines, type R and type S [#permalink] New post 10 Jan 2014, 09:24
enigma123 wrote:
A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hrs and a machine of type S does the same job in 18 hours. If the company used the same number of each type of machine to do the job in 2 hours, how many machines of type R were used?

A. 3
B. 4
C. 6
D. 9
E. 12


2x/36 + 2x/18 = 1

x = 6

C
Re: A company has two types of machines, type R and type S   [#permalink] 10 Jan 2014, 09:24
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