Answer¶
We use the formulae from iterated expectation to calculate these.
\[
\begin{alignat}{2}
P_{Y}(y) &= \begin{cases} \frac{1}{3} &y = 1\newline
\frac{2}{3} &y = 2 \end{cases}\newline
E[X] &= E[E[X \vert Y]] = \sum_{y}E[X \vert Y]P(Y)\newline
&= 90 \times \frac{1}{3} + 60 \times \frac{2}{3}\newline
Var(X) &= E[Var(X \vert Y)] + Var(E[X \vert Y])\newline
&= \sum_{y}Var(X \vert Y)P(Y) + ((90-E[E[X \vert Y])^{2}\frac{1}{3} + (60-E[E[X \vert Y]])^{2}\frac{2}{3})\newline
&= \frac{650}{3}
\end{alignat}
\]