Board Thread:Plants vs. Zombies Heroes/@comment-27101994-20170405125546/@comment-4024597-20170409153215

Here is the solution to the Cereal Box Prize problem: How many cereal boxes do you need to buy on average to get all N possible prizes. This is similar to getting Super-Rares and Legendaries (the former depends on how many multipacks you buy), but not Heroes because you can't have more than one copy of a hero. We have to count the probabilities involved in getting them as well, e.g. divide B by 0.1 since the chance of getting a Legendary is 10% for every pack.

tl;dr The average number of single packs needed to get at least one copy of each Legendary is 720