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

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Manager
Joined: 28 May 2009
Posts: 156
Location: United States
Concentration: Strategy, General Management
GMAT Date: 03-22-2013
GPA: 3.57
WE: Information Technology (Consulting)
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Kudos [?]: 233 [1] , given: 91

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

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05 Feb 2013, 17:04
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Difficulty:

25% (medium)

Question Stats:

75% (02:06) correct 25% (01:30) wrong based on 191 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 [?]: 15116 [3] , given: 224

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

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05 Feb 2013, 21:29
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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, 22:43
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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06 Feb 2013, 00:56
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, 05:19
1
KUDOS
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]

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27 Feb 2017, 05:30
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Re: A company has two models of computers, model M and model N [#permalink]

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01 Mar 2017, 18:20
1
KUDOS
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

We are given that the model M computer can complete a task in 18 minutes; thus the rate of model M is 1/18. We are also given that a model N computer can complete the same task in 9 minutes; thus the rate of model N is 1/9.

We need to determine the number of each model of computer used if the task were completed in 1 minute. If that is the case, then the combined rate of all the computers is 1/1 = 1. We can let n = the number of computers used for each model of computer and create the following equation:

rate of n model M computers + rate of n model N computers = 1

n(1/18) + n(1/9) = 1

Multiplying the entire equation by 18, we have:

n + 2n = 18

3n = 18

n = 6

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

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02 Mar 2017, 12:16
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 c=number of pairs
combined rate=1/6
c=6 pairs=6 model M computers
Re: A company has two models of computers, model M and model N   [#permalink] 02 Mar 2017, 12:16
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