GMAT Prep Question DS....Please help

[dhanda.arun]

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The correct answer is C

This is the working:
Stem 1 - Insufficient because it does not give us sufficient information;n could be 1,3,5 etc

Stem 2 - Insufficient because it does not give us sufficient information;n could be 1,5,7 etc.

But when we combine both stems we get;
n= 5,7,11,13,17,19 etc & no matter whichever odd number we take which doesnt have 3 as a factor will be divisible by 24 and hence we get the answer that r is 0.Therefore both statements are sufficient.