N is n independent events, and p is the probability of success.

Expected E(X)=np

Variance D(X)=np( 1-p)

For two-point allocation:

Expected E(x)=p

Variance D(x)=p( 1-p)

For discrete random variables:

If Y=ax+b is also discrete, then

E(Y)=aE(x)+b

D(Y)=(a^2)*D(x)

For hypergeometric distribution, describe the number of times to extract n objects from a limited number of n objects (including m objects of a specified kind) and successfully extract objects of a specified kind (without putting them back).

hope

discrepancy

The relationship between the two is

D(X)=E(X^2)-(E(X))^2