Q1 .A bag contains 9 white and 3 black balls.one ball is drown at random .Find the probability that to drown black colour balls .

probability = P (E)

Happening event = n(E) = 3

Total event = n(S) = 12

FORMULA OF PROBABILITY

P(E) = n(E) / n(S)

P(E) = 3 / 12

P(E) = 1 / 4

Probability to drown black colour balls 1 / 4

Q2 .A bag contains 9 white and 3 black balls.two ball are drown at random .Find the probability that they are of the same colour .

probability = P (E)

Total event = n(S) = ^(a+b)c₀ = ¹²c₂ = (12 * 11) / ( 2 * 1) = 66

Happening event = n(E) = ⁹c₂ + ³c₂ = (9 * 8) / ( 2 * 1) + ( 3 * 2) / ( 2 * 1) = 39

P(E) = n(E) / n(S)

P(E) = 39 / 66

P(E) = 13 / 22

Probability to drown two same colour balls is 13 / 22