1. Feb 23, 2012

### shawn26

1. The problem statement, all variables and given/known data
Problem H-10. We will compute the mean of the geometric distribution. (Note: It's also possible to
compute E(X^2) and then Var(X) = E(X^2)−(E(X))^2 by steps similar to these.)

(a) Show that
E(X) = (k=1 to infinity summation symbol) (k *q^k−1* p)
where q = 1−p.

(b) Show that the above summation can be rewritten as follows:
E(X) = p* d/dq (k=1 to infinity summation symbol) q^k

(c) The sum in part (b) is a geometric series. Evaluate the geometric series; replace the sum in (b) by this value; and do the derivative d/dq. The final answer will be a quotient of polynomials involving p
and q; there will not be an in nite sum remaining.

(d) Plug in q = 1−p and simplify to get the final answer.

2. Feb 23, 2012

### kai_sikorski

hi shawn,

Welcome to the forums.

You need to show an attempt at a solution before we can help you.

3. Feb 23, 2012

### shawn26

kinda how no clue how to go about it let me think about it a little more and get back