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Ratio of pools

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by neeti2711 » Tue Feb 28, 2017 7:18 am
The ratio of the volumes of two empty pools is 5 : 3. If the smaller pool is filled and emptied into the larger pool, what is the ratio of filled volume to empty volume in the pools?
(A) 1 : 4
(B) 2 : 5
(C) 3 : 5
(D) 3 : 8
(E) 5 : 8

OA: D

Is this a typical GMAT question? I am not certain of the source's authenticity
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by DavidG@VeritasPrep » Tue Feb 28, 2017 7:55 am
neeti2711 wrote:The ratio of the volumes of two empty pools is 5 : 3. If the smaller pool is filled and emptied into the larger pool, what is the ratio of filled volume to empty volume in the pools?
(A) 1 : 4
(B) 2 : 5
(C) 3 : 5
(D) 3 : 8
(E) 5 : 8

OA: D

Is this a typical GMAT question? I am not certain of the source's authenticity
An official question would have to be far more clearly worded than this one. Say we started with the initial scenario

Large empty pool capacity: 5x
Small empty pool capacity: 3x
Total empty pool capacity: 8x

Well, if you fill the small pool, there will be 3x units of water in the small pool and no water in the large pool. If you emptied that 3x into the larger pool, now you'd have 3x of the 5x of that large pool filled, (and 2x excess capacity) along with an empty small pool. So what is this question asking for? Do they want the ratio of water currently in the large pool to the previously empty total capacity of both pools? (This would give you a ratio of 3x/8x or 3/8.) Do they want the ratio of the currently filled portion of the large pool to the currently unfilled portions of both pools? (If there's 2x excess capacity in the large pool and 3x in the empty small pool, this would give you a ratio of 3x/(2x + 3x) = 3x/5x = 3/5.) Why would it matter that we've transferred the water from the small pool to the large if the question is asking about the total water amount of both pools? Unless there's something I'm missing here, I'd ignore this one.
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by [email protected] » Tue Feb 28, 2017 11:55 am
Hi neeti2711,

This question can be solved by TESTing VALUES.

The ratio of volume 'capacity' in two empty pools is 5:3, so let's TEST

Large pool = can hold 5 liters
Small pool = can hold 3 liters

If we fill the small pool, then empty that volume into the large pool (that step does not actually impact the math involved at all), the 3 liters of the 8 total liters of capacity are filled. The question asks for the ratio of 'filled' volume to empty volume in the pools. Since 3 liters are 'filled', 5 liters are 'empty.'

Final Answer: C

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by Jay@ManhattanReview » Tue Feb 28, 2017 9:45 pm
neeti2711 wrote:The ratio of the volumes of two empty pools is 5 : 3. If the smaller pool is filled and emptied into the larger pool, what is the ratio of filled volume to empty volume in the pools?
(A) 1 : 4
(B) 2 : 5
(C) 3 : 5
(D) 3 : 8
(E) 5 : 8

OA: D

Is this a typical GMAT question? I am not certain of the source's authenticity
Hi neeti2711,

Yes, this question falls within the scope of the GMAT.

I see that the math part in the question is quite easy. Sometime in word problems, the language plays a vital role, making a question look difficult.

The situation is the this: there are two empty pools having the capacities of 5 unit and 3 units, respectively; together they make 8 units.

Let us understand the question sentence by sentence...

If the smaller pool is filled... [Let's assume that it is filled completely]

Since only the smaller pool is filled, the combined filled volume of the pool would be 3 units as the larger pool is still empty.

...and emptied into the larger pool

Whether the 3 unit water remains in the smaller pool, in the larger pool, or partly in both, the total filled volume of both the pools still remains 3 units.

Adding a detail "...and emptied into the larger pool" has no bearing on the question, though it tests your verbal and logical ability.

=> The ratio of filled volume to empty volume in the pools = [spoiler]3/8[/spoiler]

The correct answer: D

Hope this helps!

Relevant book: Manhattan Review GMAT Word Problems Guide

-Jay
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by neeti2711 » Wed Mar 01, 2017 6:07 am
Thank you David, Rich and Jay!

I agree with David that the question is a bit ambiguous. I chose C as the answer. I still feel that to get 3:8 as the answer, the question should be differently worded. I guess the source isn't reliable.
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by ceilidh.erickson » Wed Mar 01, 2017 9:05 am
Neeti, what is the source of this question? Posters - please ALWAYS post your sources, for exactly this reason!

The content of the question (comparing two ratios) is definitely within the scope of the GMAT. However, as David pointed out, the wording is terrible!

"Volume" cannot be discussed in the abstract - it must be the measurable amount of a liquid, gas, or pourable solid (e.g. sand). A pool does not have "volume," it has "capacity": potential volume of water when filled to the top. We can talk about volume of water within a pool, but not the volume of the pool itself. And "empty volume" is completely meaningless!

Any source that writes questions this carelessly worded is not a good source to study from, as it will not give you a good indication of what the real test will be like.
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by Matt@VeritasPrep » Wed Mar 01, 2017 2:45 pm
My guess was that our author, Humpty Dumpty, meant "filled volume" to signify the amount of water in both pools combined and "empty volume" to signify the remaining space in both pools combined ... but then that wasn't the answer, even though it was an answer choice! Yuck. (Maybe I'm neglecting "unfilled volume", with the equation "unfilled volume" + "filled volume" = "empty volume"? What on earth is going on here?)
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by neeti2711 » Thu Mar 02, 2017 12:02 am
Ceilidh,

The source of the above question is bellcurves.com. I read about this source on the experience shared by an 800 scorer on this website. I started solving the questions, but these questions were not as perfect as OG questions and the answer explanations were vague.

Thank you for your help! Now I have stopped visiting this site.
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