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Machines X and Y work at their respective constant rates.

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Director
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Machines X and Y work at their respective constant rates. [#permalink] New post 14 Jun 2007, 23:13
Machines X and Y work at their respective constant rates. How many more hours does it take machine Y,working alone, to fill a prodcution order of a certain size than it takes machine X,workng alone?

( i ) Machines X and Y, working together, fill a production order of this size in two-thirds the time that machine X, working alone, does.

(ii) Machine Y, working alone, fills a production order of this size in twice the time that machine X, working alone, does.
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Re: Prep question [#permalink] New post 15 Jun 2007, 06:45
LM wrote:
Machines X and Y work at their respective constant rates. How many more hours does it take machine Y,working alone, to fill a prodcution order of a certain size than it takes machine X,workng alone?

( i ) Machines X and Y, working together, fill a production order of this size in two-thirds the time that machine X, working alone, does.

(ii) Machine Y, working alone, fills a production order of this size in twice the time that machine X, working alone, does.


Let hx and rx be respectively the number of hours needed by machine x and its rate, and hy and ry the number of hours required by machine y and its rate.

To produce P, machines x and y require respectively hx and hy hours;

P = hx*rx = hy*ry => Ratio = hx/hy = ry/rx

(i) translates into : P = (rx+ry) * h = rx * h' = (rx+ry) * 2/3 * h'
hence Ratio = rx - 2/3 rx = 2/3 ry => ry /rx =2

(ii) translates into : P = ry * h = rx *h' = ry * 1/2 * h
hence : Ratio = ry/rx = 2

Both statements are enough to calculate that it takes twice more time to machine X for the same production.

What is teh OA ?

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 [#permalink] New post 15 Jun 2007, 11:23
I have to agree with D, but I'm concerned that we're not answering the question of "how many more hours does it take". Can we say that because we know that it takes Y twice as long as X that it takes Y X's amount of hours more than X to finish the job? Is this a good enough answer for this question?

What's the OA? Thanks!
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 [#permalink] New post 15 Jun 2007, 11:25
You don't solve DS questions :)) You see whether they can be solved or not!
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 [#permalink] New post 15 Jun 2007, 13:18
I would answer E!

Question specifically asks that "how many hours it would take?". which we can not anser given the information.
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 [#permalink] New post 15 Jun 2007, 13:34
ankita wrote:
I would answer E!

Question specifically asks that "how many hours it would take?". which we can not anser given the information.


Now that I look closer - you are right Ankita!

both statements tell us the same thing - y=2x, still two variables, ans E!
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 [#permalink] New post 15 Jun 2007, 18:21
Yes, that was what I was trying to say....we are not actually answering the question asked. Thanks to Ankita for phrasing it better.
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 [#permalink] New post 20 Jun 2007, 07:47
ankita wrote:
I would answer E!

Question specifically asks that "how many hours it would take?". which we can not anser given the information.


Well, you are right. How many more hours is not how many times more hours...

When quant mixes up with verbal...
  [#permalink] 20 Jun 2007, 07:47
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