1. The problem statement, all variables and given/known data Use the Poisson distribution W=(λ^n/n!)*e^-λ to calculate <n> 2. Relevant equations <n>=ƩW*n 3. The attempt at a solution Since W = (λ^n/n!)*e^-λ I wind up with <n>=[(λ^n/n!)*e^-λ]*n But I really don't know where to go from here. Should I do a Taylor Series. I've tried crossing out the top n and ended up with [(λ^n/(n-1)!)*e^-λ] but this doesn't seem to help. If anyone can point me in the right direction or a general problem solving strategy that would be great. I'd like to demonstrate more work but I don't know what to do.