... I'm having trouble with it anyway, even though I think it might just be high school review, so I wasn't entirely sure where to put this topic. Anyway:
There are 15 items. Four are type A, five are type B, and six are type C. Selecting 3 randomly, what is the chance that exactly 2 will be type C?
There is no item replacement and it's unordered.
Since there are more questions using the same sort of thing later I was hoping to get a formula/method I could use with larger numbers instead of tracing through a diagram and multiplying every time.