What is the binomial probability rule?

Answer 1

• Suppose you have n repetitions of an experiment with only two possible outcomes each time: success and failure,
• Suppose the probability of success at any trial is independent of the outcomes of other trials and is a constant, p.

Then, the probability of exactly r successes (0 < r < n) is

[nCr]*p^r*(1-p)^(n-r) where nCr = n!/[r!*((n-r)!].

n! stands for n factorial [=fact(n) in Excel] and is equal to 1*2*...*n and 0! = 1.