#### tallstar27

##### Skeletron Prime

So, I want to get all the dev armor sets, and I was wondering what the probability of that happening was, so I could plan how many summon items to acquire. The results actually scared me a lot so I was hoping I did something wrong and someone could help me figure this out.

To start: there are 14 dev armor sets (http://terraria.wiki.gg/Developer_items; Cenx has 2 separate sets) that drop at 0.5% or 1/20 from each treasure bag. That means the odds of getting a new dev set is (1/20)*([14-n]/14), where n is the number of sets you already have.

I'll present the formula I came up with and how I simplified it.

{1/20}*(14/14)*{1/20}*(13/14)*{1/20}*(12/14)*...{1/20}*(1/14)

({1/20}^14)*[(14/14)*(13/14)*(12/14)*...(1/14)]

({1/20}^14)*((1/14)^14)*[14*13*12*...1]

({1/20}^14)*((1/14)^14)*14!

This equation yields 4.78846e-24, or 0.00000000000000000000000478846 (that's 23 zeroes after the decimal point), which as far as I can tell (no decimal to fraction site I could find would handle such a small number) is roughly 1 in 250,000,000,000,000,000,000,000.

Someone

*please*tell me I did something wrong, because I don't really want to fight 250 sextillion Duke Fishron.