If each of the stamps Carla bought cost 20, 25, or 30 cents and she bo

Total Money spent = 20a + 25 b + 30c

Question: b = ?

STatement 1: 20a + 25 b + 30c

We know, a, b and c have min value = 1

If we take our price of one stamp of each type
total money spen on them = 20+25+30 = 75 cents

Remaining money = 145 - 75 = 70

Which can be distributed as 20-20-30 or 20-25-25 i
i.e. different values of b hence

NOT SUFFICIENT

STatetement 2: a+b+c = 6

i.e. {a, b, c} will be {2, 2, 2} or {1, 2, 3} not in this order essentially hence

NOT SUFFICIENT

Combining the statements

{2, 2, 2} is NOT possible as total money spent won't be 145 cents in that case

i.e. One possible choice is a = 2, b = 3, c = 1

Second possible choice is a = 3, b = 1, c = 2

NOT SUFFICIENT

Answer: Option E
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Target question: What is the number of 25-cent stamps that she bought?

Tricky question!!
We can quickly see that statements 1 and 2 alone are not sufficient.
The hard part comes when we COMBINE the statements.

Statements 1 and 2 combined
After examining some possible scenarios, we get these two conflicting cases:
Case a: Carla bought 2 20-cent stamps, 3 25-cent stamps, and 1 30-cent stamp (6 stamps for a total of 145 cents). In this case, the answer to the target question is Carla bought 3 25-cent stamps
Case b: Carla bought 3 20-cent stamps, 1 25-cent stamp, and 2 30-cent stamps (6 stamps for a total of 145 cents). In this case, the answer to the target question is Carla bought 1 25-cent stamp
Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer: E

Cheers,
Brent
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Bunuel

Is this a new GMAT prep question? I did not see in the collection in the webiste.

Carla bought at least one of each denomination. At a minimum, she has 75 cents of stamps (30, 20, 25)

(1) If she spent a total of $1.45, we already know 75 cents consists of one of each stamp.

We have 70 cents unaccounted for; she could have purchase a 30 cent stamp and 2 20 cent stamps or 2 25 cent stamps and 1 20 cent stamp. INSUFFICIENT.

(2) We have no idea what these 6 stamps consist of; INSUFFICIENT.

(1&2) The two scenarios mentioned for statement 1 still apply here. INSUFFICIENT.

Answer is E.
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GMATinsight Bunuel chetan2u I don't get why we CAN distribute 20 for instance to 25y (see highlighted part above) if y has to be an INTEGER. Can you explain?
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BrentGMATPrepNow can you help with ST1? I get this equation 4x+5y+6z=29 and nothing seems to work, no matter what values I plug into it.
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Your equation, 4x+5y+6z=29, is correct.
Two possible solutions are:
1) x = 2, y = 3 and z = 1
2) x = 3, y = 1 and z = 2
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GMATNinja, what may be the most efficient approach to quickly come up with 2,3,1 and 3,1,2 combination under time constraint? I kept listing different combinations. However, I did not get into these two combinations because i run out of time. How can we train ourselves to quickly come up with the right combination under time constraint?

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