how would you do a random variable problem like this
suppose a non bias coin was tossed two times
Well... let $\displaystyle x$ be the random variable. You could make it stand for the number of times heads appeared.
$\displaystyle Pr(X=x)$ would then be the probability that x heads appeared.
$\displaystyle Pr(X=0) = 1-\left(\frac{1}{2}\right)^2 = \frac{3}{4}$xxx
$\displaystyle Pr(X=1)=\frac{1}{2}$
$\displaystyle Pr(X=2) = \left(\frac{1}{2}\right)^2 = \frac{1}{4}$
Since the coin is non-biased these same probabilities would appear if you set $\displaystyle x$ as the number of tails that appeared.
Is this what you wanted?