# How many random samples needed to pick all elements of set? [duplicate]

This question already has an answer here:

If repeatedly picking a random element from a set, what is the expected number of times I'd have to pick before seeing all the elements of the set?

Edit: when picking an element, it is simply counted and not removed from the set, so it can be picked again.

## marked as duplicate by joriki, Shailesh, Daniel W. Farlow, Claude Leibovici, M. VinayJun 18 '16 at 4:24

This is the coupon collector's problem. The expected number of picks required to choose all the elements of the set is $$nH_n = n\sum_{i=1}^n\frac1i.$$