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

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SVP
Joined: 21 Jul 2006
Posts: 1512

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A company has two types of machines, type R and type S.  [#permalink]

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07 Dec 2007, 06:30
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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 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

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VP
Joined: 08 Jun 2005
Posts: 1144

Kudos [?]: 246 [1], given: 0

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07 Dec 2007, 06:57
1
KUDOS
Type R = 1/36 of the job ---> In one hour
Type S = 1/18 of the job ---> In one hour

Type R = 2/36 of the job ---> In two hours
Type S = 2/18 of the job ---> In two hours

2/36+2/18 = 6/36 = 1/6

we will need six machines

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Director
Joined: 26 Jul 2007
Posts: 535

Kudos [?]: 180 [0], given: 0

Schools: Stern, McCombs, Marshall, Wharton

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07 Dec 2007, 08:47
KillerSquirrel wrote:
Type R = 1/36 of the job ---> In one hour
Type S = 1/18 of the job ---> In one hour

Type R = 2/36 of the job ---> In two hours
Type S = 2/18 of the job ---> In two hours

2/36+2/18 = 6/36 = 1/6

we will need six machines

I got the same as killer

R*T=W

(1/36x+1/18x)(2)=1
(x)(1/36+1/18)(2)=1
(x)(3/36)(2)=1
(x)(1/6)=1
x=6

Ans C

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SVP
Joined: 21 Jul 2006
Posts: 1512

Kudos [?]: 1005 [0], given: 1

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07 Dec 2007, 08:56
OA is C

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07 Dec 2007, 08:56
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