Thread:KittehWizard/@comment-6247700-20130201021838/@comment-4830404-20130320154801

A generic formula for what Khanivour is saying (so that you don't have to keep breaking down branching things over and over for large amounts of tries) is:

s = 1 - (1 - p) ^ n

Where s is probability of success after n number of tries, p is the independent chance of success on each roll, and n is the number of tries.

As number of tries increases, the probability of failing n number of times decreases. You subtract this from 1 to get your desired info, which is probability of success after n number of tries.

If you plug in Khanivour's numbers as an example, you can calculate the same probability of getting at least one Heads after two flips:

s = 1 - (1 - .5)^2

s = 1 - .25

s = .75