General question - Permutation vs. Combination

Hi Karishma,

Thanks for sharing the link -- I found it very informative. I feel like I understand it a *little* better and I know exactly what to do once I figured out if it was a permutation vs. a combination problem. My challenge still comes in in making that differentiating.

The example you had about 5 seats and 3 people, that required us to "arrange" in a sense but a very similar problem where we had to choose 3 out of 5, we had to "unarrange". I guess my biggest disconnect is what was the trigger that we had to arrange? Was it because they had given us seats?

Is it safe to say that when the GMAT wants us to PUT something/something IN/ON something -- that usually means that it's an arrange problem, hence a permutation problem?

A random question that I just thought might be relevant? I'm going to paraphrase here but it went something like, "There are 3 red marbles and 7 blue. We pick 3, what is the probability of picking at least 2 blue". I understand that we are adding a probability scenario here but if we just talk about the "favorable outcomes/numerator" and talk about the different combinations, why is it that we have to "arrange" BBR, BRB, RBB when we use the probability equation -- (7/10)(6/9)(3/8) + (7/10)(3/9)(2/8) + ... BUT if we use a Combination/Permutation equation, we don't have to arrange, meaning, we can solve by doing (7C2)(3c1) but we don't need to account for if it's BBR, BRB etc.

Sorry for the long winded question but I hope this helps clarify the topic for other users as well.

Thanks a ton,
Russ