Assuming I have A number of individuals who are randomly distributed into N number of groups. What is the probability of finding A (or any number a <= A) by picking M number of groups within N?
I figured that there are P(M, A) ways that the individuals can be distributed into the M groups. But I have no ideas how to move on from here.
Should it be conceived as:
Pr(Choosing M out of N | all of A are inside M)?
How should I compute the individual terms?