What are the variance and standard deviation of a binomial distribution with N=124 and p=0.85?

1 Answer
May 3, 2016

The variance is sigma^2=15.81 and the standard deviation is sigma approx 3.98.

Explanation:

In a binomial distribution we have quite nice formulas for the mean and wariance:
mu=Np\ \ \ \ \ \textr and\ \ \ \ \ sigma^2=Np(1-p)

So, the variance is sigma^2=Np(1-p)=124*0.85*0.15=15.81.
The standard deviation is (as usual) the square root of the variance:
sigma=sqrt(sigma^2)=sqrt(15.81) approx 3.98.