Hi All,
For Test Takers who know the Combination Formula, this question is a fairly straight-forward prompt. If you DON'T know the Combination Formula though, then here's what it is and how to use it. Any time a prompt asks for "groups" or "combinations" of things, then the order of the things DOES NOT MATTER.
For example, if a 2-person team consists of A and B, then A,B is the same as B,A --> thus, order does NOT matter. Mathematically though, you're allowed to count this team TWICE - A,B and B,A are the same team, so it should only be counted ONCE. The Combination Formula removes all of the "duplicates", leaving you with the unique combinations for whatever situation you're working with.
The Combination Formula itself is:
N!/[K!(N-K)!]
N = the total number of items/people
K = the size of the subgroup
Here, we have 10 people and we're asked to form 2 groups of 5.
For the first group, N = 10 and K = 5....
10!/[5!5!] = (10)(9)(8)(7)(6)/(5)(4)(3)(2)(1) = 256 unique groups of 5 people
Once you have formed that group of 5, then the remaining 5 form the other group (so there's no more math to do)
Final Answer: C
GMAT assassins aren't born, they're made,
Rich
