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Hoses X and Y simultaneously fill an empty swimming pool tha

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The Official Guide For GMAT® Quantitative Review, 2ND Edition

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?

(1) Hose X alone would take 28 hours to fill the pool.
(2) Hose Y alone would take 36 hours to fill the pool.

Data Sufficiency
Question: 47
Category: Arithmetic Arithmetic operations
Page: 156
Difficulty: 600


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SOLUTION

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?

We have the amount of the work to be done, hence to answer the question we need the rates of both hoses X and Y.

(1) Hose X alone would take 28 hours to fill the pool. We have the rate of hose X only. Not sufficient.
(2) Hose Y alone would take 36 hours to fill the pool. We have the rate of hose Y only. Not sufficient.

(1)+(2) We have both rates. Sufficient.

Answer: C.
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Re: Hoses X and Y simultaneously fill an empty swimming pool tha [#permalink]

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New post 21 Jan 2014, 08:40
Hose X fills 1/28 pool in one hour.
Hose Y fills 1/36 pool in one hour.

Combine X and Y will fill 1/28+1/36 pool in our.Say this comes out to be (a/b) pool in one hour.

To fill full pool it will require 1/(a/b) hours which is b/a .

So answer is (D)

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New post 22 Jan 2014, 13:44
Answer has to be (C).

Rate-work-formula: R*T=W
W = 50,000 liters

Rx = Rate of hose x
Ry = Rate of hose y
Rt = Combined rate of both hoses = Rx + Ry

Question: Given Rt * T = 50,000 what is T?

Statement (1) allows you to calculate Rx: Rx = 50,000/26. But you have no information about Ry. Not sufficient.
Statement (2) allows you to calculate Ry: Ry = 50,000/36. But you have no information about Rx. Not sufficient.

Combined, you can calculate each rate and add them to get Ry. You then can calculate the time T = 50,000/Rt.

You actually do not need to do any of these calculations. Just imagining the requirement in your head (without even writing down anything), you can see quickly that answer is C.

Btw. I feel question is Sub-600 difficulty.

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Re: Hoses X and Y simultaneously fill an empty swimming pool tha [#permalink]

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New post 22 Jan 2014, 13:46
beatthegmat05 wrote:
Hose X fills 1/28 pool in one hour.
Hose Y fills 1/36 pool in one hour.

Combine X and Y will fill 1/28+1/36 pool in our.Say this comes out to be (a/b) pool in one hour.

To fill full pool it will require 1/(a/b) hours which is b/a .

So answer is (D)


Your answer includes "b/a hours", which is a variable. I think the question asks for a specific number of hours.
You need both statements to get that.

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Re: Hoses X and Y simultaneously fill an empty swimming pool tha [#permalink]

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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?

(1) Hose X alone would take 28 hours to fill the pool.
(2) Hose Y alone would take 36 hours to fill the pool.

Data Sufficiency
Question: 47
Category: Arithmetic Arithmetic operations
Page: 156
Difficulty: 600


l]

Each week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution.

We'll be glad if you participate in development of this project:
1. Please provide your solutions to the questions;
2. Please vote for the best solutions by pressing Kudos button;
3. Please vote for the questions themselves by pressing Kudos button;
4. Please share your views on difficulty level of the questions, so that we have most precise evaluation.

Thank you![/textarea][/quote]


The answer is C. The solution is as follows.
1.(1) Hose X alone would take 28 hours to fill the pool - Insufficient as we are not aware at what rate the other hose fills the pool (Its like when two persons are doing the work we cant calculate how much time it takes to complete as we donot know the other persons working capability)
2.(2) Hose Y alone would take 36 hours to fill the pool. -- Insufficient
Now considering both 1 & 2 we know what rate both hose fill and will be sufficient to answer the question.
The quantitative solution is as follows.
Hose X fills tank in 28 hours so it fills 1/28 of the tank in an hour.
Hose Y fills tank in 36 hours so it fills 1/36 of tank in an hour.
they both together fills (1/28) +(1/36) =(16/252) =4/63. i.e they together fill 4/63 of tank in an hour.
To fill entire tank simultaneously they take 63/4 hours .
Hope only concept is sufficient to answer the question
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let A be the Hours taken by hose X alone to fill the pool.
Let B be the hours taken by hose Y alone to fill the pool.

So working together the time taken to fill the pool is given by \(\frac{1}{A}+\frac{1}{B}=\frac{1}{T}\)
Where T is the time taken together to fill the pool.

(1) Hose X alone would take 28 hours to fill the pool.
We are given A no info of B insufficient.

(2) Hose Y alone would take 36 hours to fill the pool.
we are given B no info of A insufficient.

1+2

we have both A and B hence we can calculate T using
\(\frac{1}{28}+\frac{1}{36}= \frac{1}{T}\)

Sufficient
Answer C
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New post 26 Jan 2014, 09:38
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SOLUTION

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?

We have the amount of the work to be done, hence to answer the question we need the rates of both hoses X and Y.

(1) Hose X alone would take 28 hours to fill the pool. We have the rate of hose X only. Not sufficient.
(2) Hose Y alone would take 36 hours to fill the pool. We have the rate of hose Y only. Not sufficient.

(1)+(2) We have both rates. Sufficient.

Answer: C.
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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: Hoses X and Y simultaneously fill an empty swimming pool tha [#permalink]

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New post 19 Dec 2015, 13:48
One point worth mentioning here is that one actually does not require the value of total amount of work (i.e. 50,000 litres) to answer this question. The way statements I and II are written, whether the total capacity is 50,000 or 10 litres, the answer will be the same.

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Re: Hoses X and Y simultaneously fill an empty swimming pool tha [#permalink]

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New post 09 Aug 2016, 04:59
Bunuel wrote:
SOLUTION

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?

We have the amount of the work to be done, hence to answer the question we need the rates of both hoses X and Y.

(1) Hose X alone would take 28 hours to fill the pool. We have the rate of hose X only. Not sufficient.
(2) Hose Y alone would take 36 hours to fill the pool. We have the rate of hose Y only. Not sufficient.

(1)+(2) We have both rates. Sufficient.

Answer: C.



Hi everyone, I don't quite understand this. Yea I understand why you took C, but how come it is C and not D? The question says: "if the flow in each hose is independent of the flow in the other hose", doesn't that mean that if we just have one hose working (with the other hose not doing anything) we can figure out how long it takes? So as long as X OR Y is turned on (independent of each other) we can fill the pool?

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Re: Hoses X and Y simultaneously fill an empty swimming pool tha [#permalink]

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Re: Hoses X and Y simultaneously fill an empty swimming pool tha   [#permalink] 09 Oct 2017, 08:16
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