Let E1,E2,E3,E4 and E5 be the event that are surgeries are rated as very complex , Complex, routine, simple or very simple , respectively . ∴ P(E1) = 0.15 , P(E2) 0.20 , P(E3) = 0.31 , P(E4) = 0.26 , P(E5) = 0.08 P(routine or simple) = P(E3∪E4) = P(E3) + P(E4) = 0.31 + 0.26 = 0.57