The inclusion-exclusion formula for A₁, A₂ and A₃ is
P(A₁ U A₂ U A₃) = P(A₁) + P(A₂ ) + P(A₃)
-P(A₁ ∩ A₂ ) – P(A₁ ∩ A₃) - P(A₂ ∩ A₃) + P (A₁ ∩ A₂, ∩ A₃)
use the general inclusion-exclusion formula to find the probability that at least one ball got assigned to an urn with the same label
