Question

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

Answer 1

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`.