Pool x is filled up to 2/7 of it's capacity. Let's look at condition I:
It tells us that if we add all the water from Y to X, X will get filled up to 6/7 of the capacity. That means that together both pools contain 6/7 of the water to fill pool X. To equalize the amount of water in both pools we need each pool have 3/7 of the water (that is 6/7 divided by 2). Since pool Y contains 4/7 (that we know because 6/7-2/7=4/7). we know that 1/7 of the water from pool Y has to be transfered to pool X. Our answer then will be 1/7*100%.
Condition II tells us nothing about pool Y. Hence, the answer is A.

AAAHHH much better explanation than the official MGMAT.

Thanks!

very nice explanation djkvakin.

Thank you.

Regards,
Viju

djkvakin wrote:Pool x is filled up to 2/7 of it's capacity. Let's look at condition I:
It tells us that if we add all the water from Y to X, X will get filled up to 6/7 of the capacity. That means that together both pools contain 6/7 of the water to fill pool X. To equalize the amount of water in both pools we need each pool have 3/7 of the water (that is 6/7 divided by 2). Since pool Y contains 4/7 (that we know because 6/7-2/7=4/7). we know that 1/7 of the water from pool Y has to be transfered to pool X. Our answer then will be 1/7*100%.
Condition II tells us nothing about pool Y. Hence, the answer is A.

I agree with answer A, but shouldn't the amount to be transfered be 1/4 of pool Y ?
Y contains 4/7 of X => tranfering 1/7 of X means a 1/4 of Y.

asafe wrote:

djkvakin wrote:Pool x is filled up to 2/7 of it's capacity. Let's look at condition I:
It tells us that if we add all the water from Y to X, X will get filled up to 6/7 of the capacity. That means that together both pools contain 6/7 of the water to fill pool X. To equalize the amount of water in both pools we need each pool have 3/7 of the water (that is 6/7 divided by 2). Since pool Y contains 4/7 (that we know because 6/7-2/7=4/7). we know that 1/7 of the water from pool Y has to be transfered to pool X. Our answer then will be 1/7*100%.
Condition II tells us nothing about pool Y. Hence, the answer is A.

I agree with answer A, but shouldn't the amount to be transfered be 1/4 of pool Y ?
Y contains 4/7 of X => tranfering 1/7 of X means a 1/4 of Y.

I think you are right. I have been thinking about that. very good.

Any other approaches?

Another approach is to make some strategic assumptions.
Volume of Pool X = Volume of Pool Y = 7 litres/gallons or 7000 litres/gallons makes no diff.
Volume of water in X = 2 ltrs or 2000 ltrs based on full capacity assumed.
(1) water of Pool Y emptied into Pool X
Pool X is 6/7 full so it had 6 ltrs
Assuming capacity of 7 ltrs is fine cos after the water of Pool Y is emptied the denominator of the fraction is still 7. #
Easy to see that 4 ltrs have been added from Pool Y
So pool y was 4/7 full.
Adding one litre from Y to X would be enough fro both to be 3/7 full.
Sufficient
(2) pool X has a capacity of 14,000 gallons. djkvakin says that nothing is said about Pool Y but we know capacity of Pool Y = Pool X. Importantly , it does not say how much water is there in Pool Y. Hence insufficient

# if the question said that after water from Pool y is emptied in Pool x , Pool X is 9/13 full then will making assumption work ?

chipbmk wrote: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.

OA: A

Please be as detailed as possible, I have already read through the official answer from MGMAT and I am still confused. Pretend you are explaining this to a 5th grader

Thanks!

Assume total capacity of pool x =x and that of pool y =y

Current capacity of pool x = 2x/7 and that of y=a*y ('a' because we do not know what fraction of y is currently filled)

The question is
If ay - n = 2x/7 + n, then n/ay = ?

(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.

This means: ay + 2x/7 = 6x/7
Hence ay = 4x/7
Now 4x/7 - n = 2x/7 + n
Therefore n = x/7
and n/ay = x/7 * 7/4x = 25%