If two marbles are drawn at random, what is the probability that both are red?

Total number of possible outcomes
= n(S) = ¹²C₂ = (12 x 11)/2 = 66
Total number of favorable events
= n(E) = ⁴C₂
= (4 x 3) / (2 x 1) = 6
∴ Required probability = 6/66 = 1/11