Use it when: You know P(A|Bi) and P(Bi) The Bi events are mutually exclusive and exhaustive
Mutually exclusive: No two Bi's occur together Exhaustive: One of the Bi's must occur
You often use it to compute the denominator P(A) in Bayes’ Theorem.
Forgetting to check that Bi's truly partition the sample space.
(Session 2026 - 27)