A kid is carrying 15 identical but differently colored crayons in his pocket, out of these 5 are blue, 7 green and 3 yellow. If he takes out two crayons randomly from his pocket, what is the probability that they are green and yellow?

2 crayons can be drawn out of 15 in ¹⁵C₂ = 105 ways.  One green crayon and one yellow crayon separately can be drawn in ⁷C₁ = 7 and ³C₁ = 3 ways, respectively. Since they are exclusive and independent events, taking one green and one yellow crayon together will make the favourable number of ways equal to ⁷C₁ x ³C₁ = 21 ways. Hence, required probability, P = ⁷C₁ x ³C₁/(¹⁵C₂) = 21/105 = 1/5