Question
Find the variance of the number obtained on a throw of an unbiased die.
Solution
Here S = {1, 2, 3, 4, 5, 6}.
Let X denote the number obtained on the throw. Then X is a random variable which can take values 1, 2, 3, 4, 5 or 6.
Also, P(1) = P(2) = P(3) = P(4) = P(5) = P(6) = 
∴ the probability distribution of X is
Now, 
Also, 
