Question

A bag contains 5 black balls, 4 white balls and 3 red balls. If a ball is selected randomwise, the probability that it is black or red ball is
(a) 1/3
(b) 1/4
(c) 5/12
(d) 2/3

Answer 1

(d) 2/3

Out of 12 balls, one ball can be drawn in ¹²C₁ ways.
∴ Total number of elementary events = ¹²C₁ = 12
Out of fivne black balls, one black ball can be chosen in ⁵C₁ = 5 ways.
Out of three red balls, one red ball can be chosen in ³C₁ = 3 ways.
∴ Favourable number of events = 5 + 3 = 8
Hence, required probability = $\frac{8}{12}=\frac{2}{3}$