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MGMAT data suff

by ranjithreddy.k9 » Sun Jun 12, 2011 6:57 pm
A water container is full. 10% of water evaporate everyday because of heat. If no one has removed from or added to it what will be the ratio of the quantities of water yesterday and today?

I.The ratio of evaporated water to the quantity of water left over after two days is 1:4

II.The quantity of water evaporated in the last two days is 300 gallons.


A) Statement (I) ALONE is sufficient, but statement (II) alone is not sufficient.
B) Statement (II) ALONE is sufficient, but statement (I) alone is not sufficient.
C) BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D) Each statement alone is sufficient.
E) Statement (I) and (II) TOGETHER are NOT sufficient to answer the question asked, and additional data are needed
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by gmaths » Mon Jun 13, 2011 10:31 am
first of all we want the value of the ratio of the quantity of water yesterday and today....so this has to be a fraction...
let's assume the total capacity to be V gallons..
after n days we are left with V(9/10)^n gallons....
suppose we are talking about nth day as today and so our yesterday would be (n-1)th day and the water remaining that day would be V(9/10)^(n-1)....
thus the required ratio is V(9/10)^(n-1)/V(9/10)^n....
=10/9
and so the answer to this problem lies in the question itself...therefore we can say that no additional data is required to solve this particular question...
if we have to choose one of the options then we would say that both of these statements independently are sufficient to answer this...and hence D.
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by Ashley@VeritasPrep » Mon Jun 13, 2011 10:40 am
I think the wording of the question here is a *bit* ambiguous in the sentence "10% of water evaporates everyday because of heat." If this were not a data sufficiency question, I would take that to mean that every day, 10% of what remains evaporates, but it cannot mean that here, because if it did, each new day you'd have 90% of what you had the previous day, and in that case we'd be able to answer the question 10:9 without even using *either* of the statements. Since that breaks the laws of data sufficiency problems, this must actually mean that 10% of the starting amount evaporates every day, i.e. it's a constant quantity evaporating each day.

Proceeding with that knowledge, I can conclude that statement (1) is not helpful, because a 1:4 ratio is the same as 20% gone: 80% remaining, which doesn't tell us anything beyond what we knew from the setup.

Statement (2) allows me to conclude that 20% of the original quantity (= the amount evaporated over any two days) is 300 gallons, so I can deduce that the original quantity was 1500 gallons. But that's all; I still don't know where we stood yesterday or where we stand today.

Even combining the statements, if I don't know what day we're at in the process, I'll be unable to answer the question.
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by Ashley@VeritasPrep » Mon Jun 13, 2011 10:43 am
gmaths is correct in what he said -- that the answer lies in the question itself, if indeed the question means 10% of what remains (as opposed to 10% of the original) goes away each day. But if it does mean that, that's not a GMAT data sufficiency question, because on GMAT data sufficiency questions you literally can NEVER get all the way to the answer without using at least one of the statements (after all, there is no option is data sufficiency for "neither statement is necessary")!
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by finance » Mon Jun 13, 2011 1:36 pm
is this a gmat question? do they ask such questions? what's the source?
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by ranjithreddy.k9 » Mon Jun 13, 2011 4:23 pm
gmaths wrote:first of all we want the value of the ratio of the quantity of water yesterday and today....so this has to be a fraction...
let's assume the total capacity to be V gallons..
after n days we are left with V(9/10)^n gallons....
suppose we are talking about nth day as today and so our yesterday would be (n-1)th day and the water remaining that day would be V(9/10)^(n-1)....
thus the required ratio is V(9/10)^(n-1)/V(9/10)^n....
=10/9
and so the answer to this problem lies in the question itself...therefore we can say that no additional data is required to solve this particular question...
if we have to choose one of the options then we would say that both of these statements independently are sufficient to answer this...and hence D.
Even i approached in the same way..but OA is C
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