**Solution:**

Let’ say

Event that surgeries are rated as very complex

Event that surgeries are rated as complex

Event that surgeries are rated as routine

Event that surgeries are rated as simple

Event that surgeries are rated as very simple

Given that

**(a)** (complex or very complex) or

Using the General Addition Rule:

[as given] All events are independent]

**(b)** (neither very complex nor very simple)

[:By the Complement Rule]

By the General Addition Rule]

(a) complex or very complex;

(b) neither very complex nor very simple;

(a) complex or very complex;

(b) neither very complex nor very simple;