Question
A coin is biased so that the head is 3 times as likely to occur as tail. If the coin is tossed twice, find the probability distribution of number of tails.
Solution
Let p be the probability of obtaining a head when a coin is tossed once and q that of obtaining a tail
From given condition,
p = 3 q, p + q = 1
Let X denote the number of tails in two tosses of the coin, then X can take values 0, 1 and 2.
and 
∴ probability distribution of X is
