Summary: Math 140
Professor Bernardo Ábrego
Sections 5.3, 5.4
A Property of Disjoint Events
If A and B are disjoint then
P (A and B) = 0
Example. Suppose two dice are rolled. A is
the event of getting a sum of 12, B is the
event of getting two odd numbers.
What is P (A and B) ?
The only way to get a sum of 12 is (6,6) and
both numbers are even. So A and B are
disjoint and then P (A and B) = 0.
Discussion D13 (p. 318)
Suppose you select a person at random from
your school. Which of these pairs of events
must be disjoint?
a. the person has ridden a roller coaster; the