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GMATprep - working rates

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GMATprep - working rates

by Carlo75 » Thu May 22, 2008 9:02 am
Manchines X and Y work at their respective costant rates. How many more hours does it take machine Y, working alone, to fill a production order of a certain size than it takes machine X, working alone?

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

(2) 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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Source: — Data Sufficiency |
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by sxjain3 » Thu May 22, 2008 11:20 am
I will go with "E"

Solving 1 - 1/Y + 1/X = 3/(2X) (both taken 2/3 of X time
So we will get Y = 2X, which is not an absolute value to answer the question. So insufficient

Solving 2 - Y - 2X. As above we dont have an absolute value of both X or Y

Hence we cant answer the question on how many more hours would Y take.

So "e".

Thoughts?
Last edited by sxjain3 on Thu May 22, 2008 6:46 pm, edited 1 time in total.
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by Carlo75 » Thu May 22, 2008 11:31 am
I agree. The OA is E. Thanks
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by rattanas » Fri May 23, 2008 12:12 am
I think the answer is D...
1) Suppose X takes 30 minutes and the size is 120 units...so rate of X alone is 40 units/minute....its given that X+Y together fill the same size in 2/3rd time ..SO X+Y does 120 units in 20 minutes...so the rate is 120/20 which is 60 units/minute.......By this information the rate of Y is 60-40 units/minute which is 20 units/min.......SO X took 30 minutes to fill 120 units and Y will take 120/20 which is 60 minutes for the same task....hence A is sufficient to tell that 30 more minutes wil be taken by Y

2) Very simple...It says Y takes twice the time taken by X in filling the same size...

Whts The OA answer??/,.....it should be D
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by rattanas » Fri May 23, 2008 12:14 am
oops mistake take the size 1200 units and the same explanation...
I think the answer is D...
1) Suppose X takes 30 minutes and the size is 1200 units...so rate of X alone is 40 units/minute....its given that X+Y together fill the same size in 2/3rd time ..SO X+Y does 1200 units in 20 minutes...so the rate is 1200/20 which is 60 units/minute.......By this information the rate of Y is 60-40 units/minute which is 20 units/min.......SO X took 30 minutes to fill 1200 units and Y will take 1200/20 which is 60 minutes for the same task....hence A is sufficient to tell that 30 more minutes wil be taken by Y

2) Very simple...It says Y takes twice the time taken by X in filling the same size...

Whts The OA answer??/,.....it should be D
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by amitansu » Fri May 23, 2008 1:05 am
The ans would be 'E' here !!

From both the stems of course we know that Y takes twice the time than that of Y.

But the q asks here about "How many more hours does it take"by saying that it asks for specific value not times or ratio.

For example, from II we knw Y takes twice the time X takes .
I can say if X takes 20 min then Y must be taking 40 min.
Now if X takes 1hr then B would take 2 hrs. So we can't decide about specific hrs. here.
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