If one cap is picked at random, what is the probability that it is either blue or yellow?

Total number of caps = 12
n(s) = ¹²c₁ = 12
Out of ( 2 blue + 1 yellow) caps, number of ways to pick one cap n(E) = ³c₁ = 3
∴ Required probability = p(E) = n (E) / n(s) = 3/12 = 1/4