How to calculate total chance from different simultaneous chances

5C2 is just 5!/(3!)(2!) = 120, nCr is n!/(r!)((n-r)!).
If you didn't know, you can work out the probability of activating at least once is 1 - P(not activating at all).

@Shinku: I can probably work out the answer if you give me the conditions to be fulfilled
EDIT: Ninja'd

Wisdom has 5% chance of activating.
p = 0.05
q = 0.95

Buster is 4 hits, so n = 4
If we want to work out at least one proc, work out for r = 0
4C0 (0.05)^0 (0.95)^4
= 0.8145
~81.45% chance of not triggering at all, which means 18.55% of triggering at least once per 4 hits of buster.

You got ninja'ed pretty badly lol.

Look at post #3: it was posted 11 hours and 41 mins before your post. :x

EDIT: Oops. I made a mistake in that one. How on earth did I get the wrong answer using a calculator?