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OG DS - Work problem

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OG DS - Work problem

by oks » Fri Jan 09, 2009 6:23 pm
Hoses X and Y simultaneously fill an empty swimming pool that has a capacity of 50,000 liters. If the flow in each hose is independent of the flow in the other hose, how many hours will it take to fill the pool?

A. Hose X alone would take 28 hours to fill the pool
B. Hose Y alone would take 36 hours to fill the pool

OA is C, but I'm wondering why not D? Cant we set up an equation such as:

1/x + 1/y = 1/50000? where each hose fills out 1/50000 in one hour?

Thanks!
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Source: — Data Sufficiency |
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by cramya » Fri Jan 09, 2009 6:31 pm
You would need both info since they are working simultaneously so that u can add their rates to detremine the exact time.

If one is working really fast and the other really slow versus both working really fast then the time could change. We dont know by how much and to get to a single detemrinable value we need the exact rates.

Hope this helps!
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by aj5105 » Sat Jan 10, 2009 2:10 am
Cramya,

Could you please explain a bit more on this?
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by cramya » Sat Jan 10, 2009 12:58 pm
Aj,
I was saying that we need to know both the rates to know exactly how much time it took. Hence C.

Stmts by themeselves are not sufficient
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by oks » Sat Jan 10, 2009 1:51 pm
cramya, i guess i'm still confused why was the capacity of the pool is given? knowing how fast both hoses work - we can figure out the time without the pool's capacity?

if this were a problem solving question, how would you solve it?

thanks!
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by cramya » Sat Jan 10, 2009 3:26 pm
cramya, i guess i'm still confused why was the capacity of the pool is given? knowing how fast both hoses work - we can figure out the time without the pool's capacity

Yes u can find the time taken by each hose to fill the pool wiht the statements individually. The time thats asked in the question is the time it would take if they work together.For this u need to know the rates of each hose and hence its C

(1/28+1/36) * time = 50000

time = ?

Hope this helps!

Regards,
CR
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by aj5105 » Sat Jan 17, 2009 2:55 am
CR,

IMO 1/28 + 1/36 * time = 1
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by singalong » Sat Jan 21, 2012 9:38 pm
Why is Work=1?
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