Question
A coin is tossed 4 times. X is the number of heads observed. Find the probability distribution of X.
Solution
Here X denotes the number of heads obtained in three tosses of a coin. X can take the values 0, 1, 2, 3, 4.
Let p be the probability of getting a head and q be the probability of not getting a head.
P(X = 2) = p p q q + p q p q + q p p q + p q q p + q p q p + q q p p
P(X = 3) = p p p q + p p q p + p q p p + q p p p
P(X = 4) = p p p p = 
∴ probability distribution of X is
