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# A company has two models of computers, model M and model N

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Joined: 28 May 2009
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Location: United States
Concentration: Strategy, General Management
GMAT Date: 03-22-2013
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A company has two models of computers, model M and model N [#permalink]

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05 Feb 2013, 16:04
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Difficulty:

25% (medium)

Question Stats:

74% (02:05) correct 26% (01:26) wrong based on 128 sessions

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A company has two models of computers, model M and model N. Operating at a constant rate, a model M computer can complete a certain task in 18 minutes and a model N computer can complete the same task in 9 minutes. If the company used the same number of each model of computer to complete the task in 1 minute, how many model M computers were used?

(A) 2

(B) 3

(C) 6

(D) 9

(E) 12

Source: Gmat Hacks 1800
[Reveal] Spoiler: OA

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Kudos [?]: 13618 [3] , given: 222

Re: A company has two models of computers, model M and model N [#permalink]

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05 Feb 2013, 20:29
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Expert's post
megafan wrote:
A company has two models of computers, model M and model N. Operating at a constant rate, a model M computer can complete a certain task in 18 minutes and a model N computer can complete the same task in 9 minutes. If the company used the same number of each model of computer to complete the task in 1 minute, how many model M computers were used?

(A) 2

(B) 3

(C) 6

(D) 9

(E) 12

Source: Gmat Hacks 1800

Time taken by model M computer to complete 1 work = 18 mins so Rate of work of model M = 1/18 work/min
Time taken by model N computer to complete 1 work = 9 mins so Rate of work of model N = 1/9 work/min

1 work was completed in 1 min so combined rate of work of x computers of M type and x computers of N type = 1 work/min
(because Work = Rate*Time)

x/18 + x/9 = 1 (Rates are additive)
x = 6

There are only two things to remember in work rate questions:
2. Work = Rate*Time
(which implies Rate = 1/Time)
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Re: A company has two models of computers, model M and model N [#permalink]

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05 Feb 2013, 21:43
megafan wrote:
A company has two models of computers, model M and model N. Operating at a constant rate, a model M computer can complete a certain task in 18 minutes and a model N computer can complete the same task in 9 minutes. If the company used the same number of each model of computer to complete the task in 1 minute, how many model M computers were used?

(A) 2

(B) 3

(C) 6

(D) 9

(E) 12

Source: Gmat Hacks 1800

Let's say 1 work is processing 18 gb of data.

Model M : 1 gb per min

Model N : 2 gb per min

Working together, 1 M and 1 N = 3 gb per min

So, 6 times as many computers would work at 18 gb per min.

So no. of M = 6

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Re: A company has two models of computers, model M and model N [#permalink]

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05 Feb 2013, 23:56
megafan wrote:
A company has two models of computers, model M and model N. Operating at a constant rate, a model M computer can complete a certain task in 18 minutes and a model N computer can complete the same task in 9 minutes. If the company used the same number of each model of computer to complete the task in 1 minute, how many model M computers were used?

(A) 2

(B) 3

(C) 6

(D) 9

(E) 12

Source: Gmat Hacks 1800

Another copied question from Gmat hacks. Original question from GMAT Prep:

Quote:
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

Discussed here: a-company-has-two-types-of-machines-type-r-and-type-s-130108.html
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Re: A company has two models of computers, model M and model N [#permalink]

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23 Nov 2013, 04:19
M = 1 job in 18 min → 1/18
N = 1 job in 09 min → 1/9

M+N = 1/18 + 1/9 = 3/18 = 1/6

M+N = 1 job in 6 minutes.

To complete the job in 1 min will be necessary 6 M+N.

Ans C

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Re: A company has two models of computers, model M and model N   [#permalink] 23 Nov 2013, 04:19
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