What is the variance of the number of tails in the four tosses?

Explanation

1. 01

   $E(X) = 2$, and $E(X^{2}) = \frac{0 + 4 + 24 + 36 + 16}{16} = 5$.

2. 02

   $\text{Var}(X) = 5 - 2^{2} = 1$.