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# GMAT Diagnostic Test Question 27

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GMAT Diagnostic Test Question 27 [#permalink]

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06 Jun 2009, 23:09
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GMAT Diagnostic Test Question 27
Field: word problems (work problems)
Difficulty: 600

It takes computer A 6 hours and 40 minutes to finish a job. If computer B can process the same job in 10 hours, how long will it take, for both computers working together, to finish the job?

A. 6 hours and 20 minutes
B. 5 hours and 10 minutes
C. 4 hours and 40 minutes
D. 4 hours
E. 3 hours and 20 minutes
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Last edited by bb on 29 Sep 2013, 21:23, edited 1 time in total.
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Re: GMAT Diagnostic Test Question 28 [#permalink]

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06 Jul 2009, 07:01
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Explanation:
Official Answer: D

After rewriting the time needed to finish the job in minutes, we construct an equation:

$$\frac{1}{400}+\frac{1}{600} = \frac{3+2}{1200} = \frac{5}{1200} = \frac{1}{240}$$

240 minutes equals 4 hours.
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Last edited by bb on 29 Sep 2013, 21:24, edited 1 time in total.
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Re: GMAT Diagnostic Test Question 28 [#permalink]

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I calculated it using hour.

The rate of both of them working together: 1/(20/3)+1/10=1/4
Therefore, it will take them 4 hours.
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Re: GMAT Diagnostic Test Question 28 [#permalink]

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The easisets way to solve this problem is:

Comp A alone does its work in 6*60+40=400 min , or doing 15% (400/60) of its work in 1 hour
Comp B alone does its work in 10*60=600 min , or doing 10% (600/60) of its work in 1 hour

Together A&B in 1 hour perform 25% of a certain work, so to complete all - they need 4 hours.

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Re: GMAT Diagnostic Test Question 28 [#permalink]

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20 Dec 2012, 16:47
We can solve the question as such... 6/40 +10/40 = 16/40.
so, 16/40 can be reduced to 4/10 => 2/5, so 2/5 = 0.4

Answer = 4 hrs (D)
Re: GMAT Diagnostic Test Question 28   [#permalink] 20 Dec 2012, 16:47
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# GMAT Diagnostic Test Question 27

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