When three coins are tossed, the sample space is
S = {HHH, HHT, HTH, HTT, THH, THT, TTH, TTT}
‘X’ is the random variable denotes the number of heads.
∴ ‘X’ can take the values of 0, 1, 2 and 3
Hence, the probabilities
P(X = 0) = P (No heads) = 1/8;
P(X = 1) = P (1 head) = 3/8;
P(X = 2) = P (2 heads) = 3/8;
P(X = 3) = P (3 heads)=1/8;
∴ The probability mass function is
f(x) = \(\begin{cases} 1/8&for&x=0,3\\
3/8&for &x=1,2\end{cases}\)
