Sample sapce $S$ = {HH, TT, HT, TH}
Number of Heads = $X$ = 0,1,2
Probability of getting no head = $P(X=0)$ = P(TT) = $\dfrac{1}{4}$
Probability of getting one head = $P(X=1)$ = P(HT, TH) = $\dfrac{2}{4}$
Probability of getting two heads = $P(X=2)$ = P(HH) = $\dfrac{1}{4}$
∴ Probability distribution of number of heads in two tosses of a coin is as follows
| $X$ | 0 | 1 | 2 |
| $P(X)$ | $\dfrac{1}{4}$ | $\dfrac{2}{4}$ | $\dfrac{1}{4}$ |