This is a question that has been bounced around on many MANY forums. It's not a very GMAT-like question, because its language is not precise enough.
The biggest problem I see with the question is that it is unclear whether order matters.
"How many ways" could involve distinct arrangements (i.e. permutations) or merely groups (i.e. combinations). Each situation will yield a different answer.
The good news is that the GMAT is very specific in its use of language. If you see a question with words like "distinct arrangements" or "orderings", you know it must involve permutations. If you see a word like "group", you know that order does not matter, and thus combinations are used.
Rich Zwelling
GMAT Instructor, Veritas Prep