## help with a summation

Hi there,

I am having a bit of trouble with a problem,

I am trying to find the sum from 4 to infinity of:

[ ((x-5)/x) * p(x) ]

where p(x) follows a poisson distribtuon of mean 6.

I have worked out how to do it on excel, however, I dont know if there is a more simple way of working this out?

Thanks from a first time poster