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Machines X and Y work at their respective constant rates. [#permalink]

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02 May 2006, 21:43

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Machines X and Y work at their respective constant 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) machines x and y, working togther, 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.

Machine x = 1/x job per hour
Machine y = 1/y job per hour

St1:
Together, both machines does (1/x + 1/y) job per hour = (y+x)/xy job per hour. So working together, Machine x and Machine y will complete the job in xy/(y+x) hours. This is equals to 2x/3.

Equating, we have

xy/(y+x) = 2x/3
3y = 2y+2x
y = 2x

Machine y takes twice as long as x, but we do not have the exact number. Insufficient.

St2:
We know machine y takes twice as long to complete the job, but we do not have an exact number. Insufficient.

Using St1 and St2:
Insufficient. Both statements provide the same information.

Machines X and Y work at their respective constant 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) machines x and y, working togther, 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.

please explain!!!!!!

Formula for parallel work = 1 / ((1/x) + (1/y))
equivalent to x*y / x+y
so from (1)
x*y / x+y = 2/3*x

solving we get y = 2x

not enough, we know is twice the time but not how many hours more.

from (2) y = 2x

from 2 not enough, we don't know the value of x

Together, they're saying the same stuff so doesn't work

thanks a bunch.. i dont understand how you can do 2x/3 when you say machine x takes 1/x to do the job how did you get 2x/3 should it not be 2/3x?

pls explain!

just use some logic, two machines should work faster than one, (i know in the real world might not be the case) so 2x/3 = (xy/x+y)
and keep in mind that is 1/x of the work per hour

Last edited by conocieur on 02 May 2006, 22:18, edited 1 time in total.

thanks a bunch.. i dont understand how you can do 2x/3 when you say machine x takes 1/x to do the job how did you get 2x/3 should it not be 2/3x?

pls explain!

1/x is the job done per hour. The question says it takes 2/3 the time x does. Since machine x does 1/x job in 1 hour, it would do 1 job in x hours. That's why we use 2x/3 and not 2/3x.

i think i am ok with the quant now... doing three gmat prep tests(1 after reinstall) has made me comfirtable with the format... now its just the silly mistakes in english.. in sc.. i am always down to 2.. and seem to pick the wrong one... and my awa.. aarrggggggh....

going to take leave from work today and tomorrow............

i think i am ok with the quant now... doing three gmat prep tests(1 after reinstall) has made me comfirtable with the format... now its just the silly mistakes in english.. in sc.. i am always down to 2.. and seem to pick the wrong one... and my awa.. aarrggggggh....

going to take leave from work today and tomorrow............

Thats excellent., however, I am still making mistakes -
1. Silly Mistakes
2. Miss out of special cases for PS

PS... special cases? give examples.. mayvbe i can try to give my strategy... i am generally down to only mistakes in DS.. where i miss special values.. or i forget the set of numbers are just integers.. and not real numbers...

i have started rephrashing questions every time now. that has cut down some of it.

in ps.. external triangle angle property, and the arcs in circle seem to kill me.. i forget about these two properties when i am solving the problems!!!!!!

John,

Are you giving the exam again? I thought you were done with it right?

PS... special cases? give examples.. mayvbe i can try to give my strategy... i am generally down to only mistakes in DS.. where i miss special values.. or i forget the set of numbers are just integers.. and not real numbers...

i have started rephrashing questions every time now. that has cut down some of it.

in ps.. external triangle angle property, and the arcs in circle seem to kill me.. i forget about these two properties when i am solving the problems!!!!!!

John,

Are you giving the exam again? I thought you were done with it right?

I will probably give it again! Gave it one got a 690... Not quite happy. What abt you?

but i think i have given enough of gmat prep practice at home.. the only difference would be the nerves factor sitting in when i go to the test center...

I think i know the range i am going to score(if gmat prep is indicative), if i keep my nerves under control, and dont make silly mistakes..

I am going to and check the test center out today..

initially i was worried of the quant becoming harder with pearson, hence i gave myself a month more.. i am thankful i did that, because gmatprep is definitely harder than powerprep!

and from analysiing all posts here.. gmat prep and official gmat is not that much different........... so lets keep fingers crossed........................

will give a detailed report tomorrow night 9.30 pm!!!!(PST)

but i think i have given enough of gmat prep practice at home.. the only difference would be the nerves factor sitting in when i go to the test center...

I think i know the range i am going to score(if gmat prep is indicative), if i keep my nerves under control, and dont make silly mistakes..

I am going to and check the test center out today..

initially i was worried of the quant becoming harder with pearson, hence i gave myself a month more.. i am thankful i did that, because gmatprep is definitely harder than powerprep!

and from analysiing all posts here.. gmat prep and official gmat is not that much different........... so lets keep fingers crossed........................

will give a detailed report tomorrow night 9.30 pm!!!!(PST)

but i think i have given enough of gmat prep practice at home.. the only difference would be the nerves factor sitting in when i go to the test center...

I think i know the range i am going to score(if gmat prep is indicative), if i keep my nerves under control, and dont make silly mistakes..

I am going to and check the test center out today..

initially i was worried of the quant becoming harder with pearson, hence i gave myself a month more.. i am thankful i did that, because gmatprep is definitely harder than powerprep!

and from analysiing all posts here.. gmat prep and official gmat is not that much different........... so lets keep fingers crossed........................

will give a detailed report tomorrow night 9.30 pm!!!!(PST)

All the best for your test tommorrow .I will be eagerly waiting for your experience and feedback .

From st1:
A(1/x+1/y)=1 where A is time needed to fill an a production order if machine x and y work together
B(1/x)=1 where B is time needed to a production order of machine x works alone
A=2/3B
2/3(1/x+1/y)=1/x 1/x=2/y there are 2 variables in the equation, so insuff.

From st 2:
A(1/y)=1, B(1/x)=1, A=2B, so 2/y=1/x, it has also 2 variables, thus it is insuff. alone.
Since both statements gives us the same information, combining them also will not give us the answer,
So the answer is E.