# Today I Learned

Some of the things I've learned every day since Oct 10, 2016

## 26: Partial and Pseudo-Linearity of Variance

If two random variables $A, B$ are independent, then

$\textrm{Var}(A + B) = \textrm{Var}(A) + \textrm{Var}(B)$.

However, this is not true in general. It is always the case, however, that for a constant scalar $c$,

$\textrm{Var}(c A) = c^2 \textrm{Var}(A)$.