Introduction to Statistics - Fall 2006.
09:30-11:00 AM | Auditorium Wheeler
Instructor Fletcher Ibser
Tue 10/10 Probability I
Venn Diagram = Rectangle and the probability of the whole is 1
P(B/A) = Probability of B Happening Given that A has Happened.
e.g. Chance that a die rolls a 6 given that it has rolled an even number = 1/3
Multiplication Rule
Generic Case
P(A and B) = P(A) . P(B/A)
e.g. A red die rolls a 6 and a blue die also rolls a 6.
Think of it as a proportion. A large number of people do this so 6 will happen to 1/6th number of people.
Then a 6 will happen to 1/6th of that 1/6th group.
Special Case
If A and B are independent then
P(A and B) = P(A) . P(B)
Addition Rule
P(A or B) = P(A) + P(B) - P(A and B)
Venn Diagram makes it clear
This of two circles A and B overlapping so you will have to remove the overlapping portion which is what subtracting the P(A and B) does.
