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Old 2003-12-13, 02:58   #4
Orgasmic Troll
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Jul 2003

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X is a random variable with binomial distribution

The probabilty of getting n heads out of N trials with a coin that has probabilty p of coming up heads (and probabilty q=1-p of getting tails) is

(N,n)*pnqN-n = N!/n!(N-n)! * pn(1-p)N-n

where (N,n) is a binomial coefficient

the standard deviation is Sqrt[N*p*(1-p)]

Sorry if I gave too much away
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