On the GMAT, problems about multiples are generally constrained to POSITIVE multiples.
I've amended the problem to reflect how it would appear on the GMAT.

kris610 wrote: If S is a sequence of consecutive positive multiples of 3, how many multiples of 9 are there in S?

(1) There are 15 terms in S.

(2) The greatest term of S is 126.

A

Statement 1: There are 15 terms in S.
Among every 3 consecutive multiples of 3, exactly ONE will be a multiple of 9:
3,6,9
6,9,12
9,12,15
12,15,18
15,18,21
18,21,24

The 15 terms in S = 5 cycles of 3 consecutive multiples of 3.
Within each cycle, there will be exactly ONE multiple of 9.
Thus, there will be 5 multiples of 9 in set S.
SUFFICIENT.

Statement 2: The greatest term of S is 126.
Without knowing the total number of terms, we can't determine how many multiples of 9 are in set S.
INSUFFICIENT.

The correct answer is A.

Learn to recognize how the GMAT lays TRAPS.
Virtually every test-taker would recognize that given the number of terms (statement 1) and the greatest term (statement 2), we could simply count how many multiples of 9 are in set S.
If the OA is C, the question becomes TOO EASY.
Thus, the OA is probably NOT C.
Whenever C seems too obvious an answer choice, be suspicious: there is a good chance that ONE of the two statements will be SUFFICIENT on its own.

GMATGuruNY wrote:

kris610 wrote:Source Master GMAT
For starters, I'm not discussing anything about the answer except the OA (hidden).
If S is a sequence of consecutive multiples of 3, how many multiples of 9 are there in S?

(1) There are 15 terms in S.

(2) The greatest term of S is 126.

A

Statement 1: There are 15 terms in S.
Among every 3 consecutive multiples of 3, exactly ONE will be a multiple of 9:
3,6,9
6,9,12
9,12,15
12,15,18
15,18,21
18,21,24

The 15 terms in S = 5 cycles of 3 consecutive multiples of 3.
Within each cycle, there will be exactly ONE multiple of 9.
Thus, there will be 5 multiples of 9 in set S.
SUFFICIENT.

Statement 2: The greatest term of S is 126.
Without knowing the total number of terms, we can't determine how many multiples of 9 are in set S.
INSUFFICIENT.

The correct answer is A.

Learn to recognize how the GMAT lays TRAPS.
Virtually every test-taker would recognize that given the number of terms (statement 1) and the greatest term (statement 2), we could simply count how many multiples of 9 are in set S.
If the OA is C, the question becomes TOO EASY.
Thus, the OA is probably NOT C.
Whenever C seems too obvious an answer choice, be suspicious: there is a good chance that ONE of the two statements will be SUFFICIENT on its own.

-3,0 and 3 are consecutive multiples of 3 without a multiple of 9. In such a case only C is the answer..

ajithkumar wrote:-3,0 and 3 are consecutive multiples of 3 without a multiple of 9. In such a case only C is the answer..

On the GMAT, problems about multiples are generally constrained to POSITIVE multiples.
In my post above, I've amended the problem to reflect how it would appear on the GMAT.

GMATGuruNY wrote:

ajithkumar wrote:-3,0 and 3 are consecutive multiples of 3 without a multiple of 9. In such a case only C is the answer..

On the GMAT, problems about multiples are generally constrained to POSITIVE multiples.
In my post above, I've amended the problem to reflect how it would appear on the GMAT.

I have seen questions (retired gmat questions) involving negative multiples. Secondly we have option C, which will give a foolproof answer. I honestly believe that the OA given by economist is an errata.

There is no need to mention "Positive multiple as "0" is considered a multiple of every number.

https://www.manhattangmat.com/forums/num ... t4998.html

The answer must be Option-A

GMATinsight wrote:There is no need to mention "Positive multiple as "0" is considered a multiple of every number.

https://www.manhattangmat.com/forums/num ... t4998.html

The answer must be Option-A

yes, zero is a multiple of every number. the trick for the GMAT however is to read carefully what KIND of multiple they ask for. so while yes, zero is a multiple of every number, it is not a POSITIVE multiple of ANY number. usually on the GMAT they say "positive multiples of" or some other clarifying language

The question is wrong (missed the term 'positive') or the answer is 'C'.

GMAT always makes it very clear with the terminology. Secondly the the idea behind a data sufficiency problem is to look for all possible scenarios. So there is no way we can consider only +ve multiples. On what basis will you ignore -6,-3 and so on?