I am trying to evaluate the following summation:
Please look at page 3 in the book link
When he is deriving the expectation of a geometric random variable he writes E(X) as a double summation and then changes the order of summation. My doubt is when can you and when can you not reverse the order of summations and HOW DO YOU DETERMINE the limits of summation when you change the order of summation?
I did not understand how the limits of the indices j and k change when you reverse the order of summations..please help