Bunuel wrote:

Paula and Sandy were among those people who sold raffle tickets to raise money for Club X. If Paula and Sandy sold a total of 100 of the tickets, how many of the tickets did Paula sell?

Given that p+s=100, where p and s are the number of tickets sold by Paula and Sandy, respectively.

(1) Sandy sold 2/3 as many of the raffle tickets as Paula did --> s=\frac{2}{3}p. We have two distinct linear equations with two unknowns (p+s=100 and s=\frac{2}{3}p), thus we can solve for both of them. Sufficient.

(2) Sandy sold 8 percent of all the raffle tickets sold for Club X --> we don't know the total number of the raffle tickets sold, thus we cannot find s, which means that we cannot find p. Not sufficient.

Answer: A.

I believe the key premise for statement 2 is that there could be others as well who sold tickets for Club X. Right ?

Yes, we are directly told that there in fact ARE some other people selling tickets: "Paula and Sandy were