To be complete I'll just post everything about the problem.
Q: Each brand of candy bar has one coupon in it. There are n different coupons in total; getting at least one coupon of each type entitles you to a prize. Each candy bar you eat can have any one of the coupons in it, with all being equally likely. Let X be the (random) number of candy bars you eat before you have all coupons. What are the mean and variance of X?
A. So the expected value of X is a sum of geometric discrete random variables.
so you have one coupon on the first trial.
let denote the number of bars needed to get the 2nd coupon
The part Im having trouble on is the variance. From my definition:
so does that mean...
Any help is appreciated