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# If it takes 6 printing presses 4 hours to print 5000

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If it takes 6 printing presses 4 hours to print 5000 [#permalink]  08 Nov 2003, 14:43
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If it takes 6 printing presses 4 hours to print 5000 newspapers, how long should it take 3 presses to print 3000 newspapers?

A) 3 hrs., 20 min.

B) 4 hrs., 20 min.

C) 4 hrs., 48 min.

D) 5 hrs., 48 min.

E) 6 hrs., 50 min

This problem has three variables...how do we solve such problems.

Thanks your responses would be highly appreciated.

Vivek
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I vote for C

In this case, it would be useful to find how many per hour for all presses
6 -> 4 => 5000
6 -> 1 => 1250

Since we need to find out the number for 3 presses we can get away with dividing the current number by 2 to find the hourly rate.
So,
3 -> 1 => 625

Now we need to find how much time it will take to print 3000 papers:
3000 / 625
= 4.8 hrs = 4 hrs. 48 min.
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You are right..wonder_gmat
Thanks for the explanation.

Vivek.
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Re: Work PS [#permalink]  19 Nov 2003, 17:51
All these work and rate problems revolve around Volume(Quantity) proportional to rate * time. This means in two different situations, these 3 variables will be in direct or inverse proportion. So you don't have to think of them as 3 different variables and there would be no need to build 3 equations and solve.

Here, the questions asks for time in one situation. Since you know the time in some situation(first situation) put it down first and then multiply it with ratios of the remaining variables in 2 situations. See below

4 * 3000/5000 * 6/3 = 24/5

Explanation for the 3 parts.

1) 4 - time in the situation that you know
2) 3000/5000 - (Ratio of papers in 2 situations) In the second situation, there less number of papers are printed, therefore lesser time would be required. Hence the lesser number 3000 would go to the numerator.
3) 6/3 - (Ratio of presses in 2 situaions) In the second situation, there are less number of presses, so more time would be required. Hence the higer number would go to the numerator.

Supposing there was another variable in the problem, say number of hours that the presses work. Say 6 in the fist case and 8 in the second case, we would have had a fourt part

4) 6/8

get the drift...?

vivek_dj wrote:
This problem has three variables...how do we solve such problems.

Thanks your responses would be highly appreciated.

Vivek
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If it takes 6 printing presses 4 hours to print 5000 newspapers
then
3 presses in 4 hours will complete 2500 news papers. They need to finish another 500 more to reach 3000

2500 take 4 hrs
500 will take 500 * 4 / 2500 = 0.8 hrs = 48 mins
so 4 hrs 48 mins is the answer.
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Re: Work PS [#permalink]  30 Oct 2011, 10:57
6 printing presses need 4 hours to print 5000
so 3 printing presses need 8 hours to print 5000
how many hours to print 3000?
just proportion:

X=\frac{3000*8}{5000}=4.8

4 hours and 48 mins
Re: Work PS   [#permalink] 30 Oct 2011, 10:57
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