# Homework Help: Confusing Ball Problem.

1. Feb 24, 2010

### sezmin

hey, im having a lot of trouble approaching this problem:

let m balls be independently distributed into s boxes with equal probabilities
m has a poisson distribution with mean 1/b
let Xi be the number of balls in box i, i = 1,2,...,s
let y = the number of empty boxes
are X1, X2, ... , Xs independent?

i cant really conceptualize a function to describe the Xi's and cant find the joint pdf of X1,X2,...Xs

my thought was that p(Xi) = (1/s)^(Xi) * ((s-1)/s)^(m - Xi)
but, i don't see how that gets anywhere...