I may have asked this one already, but I can't remember so let's pretend it's new!
Imagine that as an avid collector of Crackerjack prizes, you set out to collect them all. Luckily, Crackerjack has scaled back on the variety of prizes available to just 4 types so the task will be less onerous than usual. You decide to order Crackerjack boxes in cases of 12 to take advantage of the savings down at Ludicrous Luke's Low-ball Local Ltd., but before you place your order you feel compelled to calculate the probability of collecting all 4 prizes at a stroke. So, how many cases would you have to order to be:
(a) at least 90% sure of collecting all 4 prizes?
(b) at least 99% sure?
(c) at least 99.9% sure?