If Pool Y currently contains more water than Pool X, and if : GMAT Data Sufficiency (DS)
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# If Pool Y currently contains more water than Pool X, and if

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DS: Pool Y and Pool X [#permalink]

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07 Dec 2010, 07:21
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If Pool Y currently contains more water than Pool X, and if Pool X is currently filled to 2/7 of its capacity, what percent of the water currently in Pool Y needs to be transferred to Pool X if Pool X and Pool Y are to have equal volumes of water?

(1) If all the water currently in Pool Y were transferred to Pool X, Pool X would be filled to 6/7 of its capacity.

(2) Pool X has a capacity of 14,000 gallons.

[Reveal] Spoiler: Doubt
Hi.

I came across this DS question on my last MgCAT, and while I do understand how to solve it, I fail to see why (according to the Mg explanation) we should consider both pools capacity as equal, when nothing in the text leads to that assumption… (or am I missing something here?)

Therefore I felt for E.

Thanks for the help.
[Reveal] Spoiler: OA
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Re: Can someone clear out this DS question for me plz. [#permalink]

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07 Dec 2010, 08:10
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itnas wrote:
Hi.

I came across this DS question on my last MgCAT, and while I do understand how to solve it, I fail to see why (according to the Mg explanation) we should consider both pools capacity as equal, when nothing in the text leads to that assumption… (or am I missing something here?)

Therefore I felt for E.

Thanks for the help.

If Pool Y currently contains more water than Pool X, and if Pool X is currently filled to 2/7 of its capacity, what percent of the water currently in Pool Y needs to be transferred to Pool X if Pool X and Pool Y are to have equal volumes of water?

(1) If all the water currently in Pool Y were transferred to Pool X, Pool X would be filled to 6/7 of its capacity.

(2) Pool X has a capacity of 14,000 gallons.

We are nowhere told that the capacities of pools X and Y are equal.

(1) If all the water currently in Pool Y were transferred to Pool X, Pool X would be filled to 6/7 of its capacity --> together pools X and Y contain 6/7 of the capacity of pool X. Now, in order pools X and Y to contain equal amount of water each pool should contain 3/7 of the capacity of pool X, thus from pool Y, which contains 4/7 (6/7-2/7=4/7) of the capacity of pool X we must transfer 1/7 of the capacity of pool X, which is 25% of the water currently in pool Y (1/7)/(4/7)=1/4. Sufficient.

Or consider the following:
Let the capacity of pool X be 7 gallons. It's 2/7 full, thus there are 2 gallons of water. If all the water currently in Pool Y were transferred to Pool X, Pool X would be filled to 6/7 of its capacity and thus will contain 6 gallons of water, which means that there are now 6-2=4 liters of water in pool Y (it doesn't matter what capacity it has). In order both pools to contain equal amount of water each pool should contain 3 gallons of water, thus we should transfer 1 gallon from pool Y to pool X. 1 gallon is 1/4 of the water currently in pool Y.

(2) Pool X has a capacity of 14,000 gallons. No info about pool Y. Not sufficient.

Hope it's clear.
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Re: Can someone clear out this DS question for me plz. [#permalink]

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07 Dec 2010, 08:22
Thanks, I guess I just got blinded by not knowing the capacity of either pools.

Your explanations just remind me the scene of Die Hard 3 when transferring gallons of water from one “jar” to another in order to disarm the bomb
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Re: Can someone clear out this DS question for me plz. [#permalink]

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07 Dec 2010, 19:36
Haha! I started reading the question and thought of the same thing... ahhhh the 90s action movies
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Re: Pool Capacity [#permalink]

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18 Sep 2011, 14:55
Lets say pool x's total capacity = x
=> Pool x filled capacity = (2/7)x

Lets say pool y's total capacity = y

lets say pool y's filled capacity = py ( where p is some fraction)

Let r be the volume transferred from y to x.

if py - r = (2/7)x+r , r is what percent of py?

1. Sufficient

py- r = (2/7)x+r = (6/7)x

(2/7)x+r = (6/7)x => r = (4/7)x

py - r = (6/7)x => py = (10/7)x

r is what percent of py? i.e is (((4/7)x) / ((10/7)x)) *100

= (4/10)*100

2. Not sufficient
we dont know anything about pool y or how much removed from pool y.

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Re: If Pool Y currently contains more water than Pool X, and if [#permalink]

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24 Jun 2013, 02:17
Bumping for review and further discussion*. Get a kudos point for an alternative solution!

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Re: If Pool Y currently contains more water than Pool X, and if [#permalink]

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24 Jun 2013, 10:33
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Bunuel wrote:
Bumping for review and further discussion*. Get a kudos point for an alternative solution!

*New project from GMAT Club!!! Check HERE

All DS Fractions/Ratios/Decimals questions: search.php?search_id=tag&tag_id=36
All PS Fractions/Ratios/Decimals questions: search.php?search_id=tag&tag_id=57

Question:
Let the capacity of X be C
so, X= 2C/7 and Y>X
If n is the quantity of water taken from Y and put into X
Then,
Y-n = X+n
2n = Y-X => n = (Y-X)/2
n is the quantity that needs to be transferred.
The % will (n/Y) * 100 %
(Note, that we already have one equation with X and C, and we just need one more involving Y and C, if we can get it out of any of the statements, it should be enough to solve)
Now lets take a look at the statements :

(1) If all the water currently in Pool Y were transferred to Pool X, Pool X would be filled to 6/7 of its capacity.

Y+X = 6C/7
and we know that X=2C/7

Hence, Y=4C/7

n = (Y-X)/2 = C/7
Therefore, % of water = (C/7)/(4C/7) *100
=100/4
=25%

Sufficient.

(2) Pool X has a capacity of 14,000 gallons.

We need another relation in Y and C or Y and X to be able to solve, not sufficient.

Ans: A
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Re: If Pool Y currently contains more water than Pool X, and if [#permalink]

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13 Sep 2014, 21:23
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: If Pool Y currently contains more water than Pool X, and if [#permalink]

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15 Jan 2016, 02:21
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: If Pool Y currently contains more water than Pool X, and if   [#permalink] 15 Jan 2016, 02:21
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