We are not concerned with order, since we just need to get people in a team.

So, we have to choose:

- at least 2 offices to 2 civilians to form a 5 member team.

So the team could compris either (3 officers, 2 civilians), or (2 officers, 3 civilians)

group 1 (3 officers, 2 civilians)
# of combinations of 3 officers picked from 5 officers = 5!/3!2! = 10

# of combinations of 2 civilians picked from 9 civilians = 9!/2!7! = 36

So # of combinations of 3 officiers AND 2 civilians = 10*36 = 360

group 2 (2 officiers, 3 civilians)
# of combinations of 2 officers picked from 5 officers = 5!/3!2! = 10

# of combinations of 3 civilians picked from 9 civilians = 9!/3!6! = 84

So # of combinations of 2 officers AND 3 civilians = 10*84 = 840

Total number of combination = 360 +840= 1200 (b)

Hope this answers you queston. I've never solved probability questions with nCr or nPr or any other complicated hypergeometric distribution equations, etc.

In fact, the proability questions on the GMAT wouldn't require you to know them, you just need to know what you're looking for. But you are expected to be able to tell when order matters and when order does not matter, along with some basic counting rules.