A die is tossed twice. A ‘success’ is getting an even number on a toss. Find the variance of the number of successes.
Let X be the random variable for a ‘success’ for getting an even number on a toss.
∴ X = 0, 1, 2
n = 2
Even number on dice = 2, 4, 6
∴ Total possibility of getting an even number = 3
Total number on dice = 6
p = probability of getting an even number on a toss
q = 1 – p
Now, the probability of x successes in n–Bernoulli trials is nCrprqn-r
Thus, P( x successes) = nCrprqn-r
=1
Also, Var(X) = E(X2) – [E(X)]2
= ΣX2P(X) – [E(X)]2
= 1.5 – 1
= 0.5