Roll one fair die. A is an even face and B is a face less than four. What is the probability of A or the complement of B?

1. Event A is the set of even faces 2, 4 and 6. 2. Event B is the set of faces 1, 2 and 3, so the complement of B is 4, 5 and 6. 3. The union of those two sets is 2, 4, 5 and 6. 4. That is four outcomes out of six, which is 4/6, or 2/3. 5. A value of 5/6 belongs to the union of A and B itself rather than of A and the complement of B. 6. A value of 1/2 would count only three of the six faces and misses one member of the union. _Source: OpenStax Introductory Business Statistics (CC BY 4.0), Ch 3 "Probability Topics", section 3.1 Terminology_