# Math Help - Computing mean and variance of geometric random variable?

1. ## Computing mean and variance of geometric random variable?

hello!

So I am given the probability mass function of a geometric random variable, denoted by p(k)=p(1-p)^k, where p is the success, and 1-p is the failure. I am suppose to compute the mean and variance using the MOMENT GENERATING FUNCTION. I need help to study for my semester midterm! Thanks

2. ## Re: Computing mean and variance of geometric random variable?

Hey weeman8.

Hint: Recall that E[X] = d/dt MGF_X(t) | t = 0 and E[X^2] = d^2/dt^2 MGF_X(t) | t = 0 where Var[X] = E[X^2] - E[X]^2