Specific Addition Rule
Only valid when the events are mutually exclusive.
P(A or B) = P(A) + P(B)
Example 1:
Given: P(A) = 0.20, P(B) = 0.70, A and B are disjoint
I like to use what's called a joint probability distribution. (Since disjoint means nothing in common, joint is what they have in common -- so the values that go on the inside portion of the table are the intersections or "and"s of each pair of events). "Marginal" is another word for totals -- it's called marginal because they appear in the margins.
The values in red are given in the problem. The grand total is always 1.00. The rest of the values are obtained by addition and subtraction.
