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# stamps

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Manager
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stamps [#permalink]  11 Dec 2008, 17:36
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Joanna bought only $0.15 stamps and$0.29 stamps. How many $0.15 stamps did she buy? (1) She bought$4.40 worth of stamps.
(2) She bought an equal number of $0.15 stamps and$0.29 stamps.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.
Manager
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Re: stamps [#permalink]  11 Dec 2008, 18:25
A

1) 0.15n + 0.29m = 4.4

The above condition holds true, only when n = m = 10.

Approach:

Usually in GMAT DS, option B is given to support or give additional clue for the option A to render the answer. Since ideally all GMAT questions real world questions i,e we get same answer for D using both the statement.(again most cases)

So by keeping this in mind, if u see option B it is giving addional clue to give solution, but if u see possible answers with option A, it can give answer only when both n=m.( since 29 is a prime and multiples of 15 cannot be equal to multiples 29 whose sum is 440).

Hope this helps some audience.
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Re: stamps [#permalink]  12 Dec 2008, 20:45
haichao wrote:
Joanna bought only $0.15 stamps and$0.29 stamps. How many $0.15 stamps did she buy? (1) She bought$4.40 worth of stamps.
(2) She bought an equal number of $0.15 stamps and$0.29 stamps.

I thought it would be worth noting why statement one is enough information since it might not be obvious that the solution of ten 15-cent stamps and ten 29-cent stamps is the ONLY solution here.

Let's use cents rather than dollars.

The most important thing to notice here is that no matter how many 15-cent stamps I buy, their total value will always end in 5 or 0 (e.g., 15 cents, 30 cents, 45 cents, 60 cents etc). So, if we are to combine a certain number of 29-cent stamps, we need enough of them so that their total value ends in either 5 or 0 since all of the stamps are worth a nice tidy sum of 440 cents.

Under what circumstances will the total value of our 29-cent stamps end in either 5 or 0? When we have 0 stamps, 5 stamps, 10 stamps or 15 stamps. We need to check all four of these cases, since it might be possible that there are two or more ways to get 440 cents worth of stamps, in which case (1) would not be enough informaiton.
If we check four cases, only one case (ten 29-cent stamps combined with ten 10-cent stamps) will give us a sum of 440 cents.

This is why statement (1) provides enough information.

Statement (2) does not provide enough information.

Re: stamps   [#permalink] 12 Dec 2008, 20:45
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