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GMATPrep DS Sample Question

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GMATPrep DS Sample Question

by wolfe05 » Sat Apr 25, 2009 1:46 pm
The answer explanation for this problem just does not seem right to me. I chose B statement 2 alone, but it says E neither are sufficient. Please explain.

In a refinery, the capacity of oil tank A is 70% of the capacity of oil tank B. How many more gallons of oil are in tank A than in tank B?

(1) Tank A is 90% full; tank B is 50% full.
(2) When full, tank A contains 50,000 gallons of oil

Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.

Answer Explanation

Since you do not know the number of gallons in either tank A or tank B, (1) alone is not sufficient. From (2) alone, you can determine the capacities of tanks A and B, but you do not know whether the tanks are full. Using (1) and (2) together, you can determine the number of gallons in A and B; therefore, BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
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Source: — Data Sufficiency |
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by mike22629 » Sat Apr 25, 2009 4:14 pm
The answer is C, which is the Answer in the explanation.

Question Stem Tells you the ratio of capacities between A and B.

1) Second quetion tells you how full each one, so you have the relationship of how much is in A to how much is in B, but you need at least one value to tell you the amounts.
Insufficient

2) This tells you that A's capacity and B's capacity via the relationship in the question stem, but you do not know how much is in each one.

Both Statements together tell you how many Gallons are in each so you can find out the difference between A and B.

This is how you work the problem:

Capacity of A = (Capacity of B)*(7/10)

Capacity of A = 50,000

50,000 = (Cap of B)*(7/10)

Cap of B = 71428.57143

(Capacity of A)(Percent Full) = Gallons in A

50000*.9 = 45000

(Capacity of B)(Percent Full) = Gallons in B

71428.57143*.5 = 35714.28571

45000 - 35714.28571 = 9285.71429

Notice that working out the problem is not necessary, but rather noticing that the information is sufficient.
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by mike22629 » Sat Apr 25, 2009 4:20 pm
If the integers "a" and "n" are greater than 1 and the product of the first 8 integers is a multiple of a^n, what is the value of a?

1) a^n = 64

2) n = 6

OA after a few responses. By the way, I got the right answer, but it took me a while, I am looking for an efficient approach.
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by mike22629 » Sat Apr 25, 2009 4:21 pm
Sorry, the second post was a question I was asking. I moved it to its own thread so it can be ignored.
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by wolfe05 » Mon Apr 27, 2009 6:32 am
Yeah, after taking some time off from the book and looking at the question again, I see where this problem is straight forward.

Thanks for the reply though.
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