# For random variables #X# and #Y#. What is #"Var"(X+Y)# in terms of #"Var"(X)# and Var(Y)?

##### 1 Answer

Oct 29, 2015

#### Explanation:

Note that

#"Var"(X+Y) = Var (X) + Var (Y) + 2"Cov" (X,Y) #

You can write

#"Var"(X+Y) = Var (X) + Var (Y) #

Only if