TITLE: Throwing All Numbers From 2 to 12 With Two Dice
QUESTION [9 upvotes]: What is the expected number of times one must throw two fair dice before all numbers from 2 to 12 have appeared at least once?

REPLY [4 votes]: This is a kind of coupon collector problem, with unequal probabilities. It has been studied, but the formula for the expected waiting time seems quite (too?) complicated. 
Here's the main paper (restricted - you can try to download it here: ftp://210.112.137.112/pub/Papers/schelling.pdf )
See also here.