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

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Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9983
Location: Pune, India
Re: A company has two types of machines, type R and type S  [#permalink]

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08 Dec 2019, 22:16
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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 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

Work done by machine R in 1 hr = 1/36
Work done by machine S in 1 hr = 1/18

If both work together, work done in 1 hr = 1/36 + 1/18 = 1/12 (this is the work done by a pair, R and S in 1 hr)

But we need them to do 1/2 work in 1 hr. So we must have 6 pairs (R and S) of them.

So 6 R machines were used and 6 S machines were used.

myhigheredmba
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Karishma
Veritas Prep GMAT Instructor

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Joined: 30 Jun 2019
Posts: 5
Re: A company has two types of machines, type R and type S  [#permalink]

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09 Dec 2019, 17:37
VeritasKarishma - Oh, I see! It's because the 6 represents pairs!! Thank you so much!
Re: A company has two types of machines, type R and type S   [#permalink] 09 Dec 2019, 17:37

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