Exercise$-4.$

$Y_n$ is an random process, and $Y_0=0,Y_n={\displaystyle \underset{i=1}{\overset{n}{}}}{x}_i$

here $x_i$ is an random variable, each $x_i$ are independent

and its outcomes are $\{-1,1\},$ besides

$P\{x_i=-1\}=q,P\{x_i=1\}=p$

Find $E[Y_n]$ and Var$[Y_n]$