1. 1.7 Addition Rule - Tree Diagrams (1/3)
P(A or B) = P(A) + P(B)
Rolling a single die twice.
P(3 and 4 in any order)
= P(3,4) + P(4,3) 1 36 1 36 2 36 1 18 = + = =
1st
toss
2nd
toss
1/6 1 6 1 6 1 36
1/6 3 4
P(3,4) = x = 1 6 1 6 1 36
1/6 4 3
P(4,3) = x =
1/6

2. Multiply along branches
1.8 Tree Diagrams (2/3)
Rules
Multiply along branches
Add branches together.

3. 1.7 Tree Diagrams Example (3/3)
A bag contains 3 red, 6 blue, 5 green and 4 white marble.
If two are chosen, with replacement, what is the probability that only one will be blue.
1/3 B
Not
P(Only one blue) =
1/3 B
Not
P(B, Not) +
P(Not, B)
2/3
1/3
2/3 B
Not =
1/3 x
1/3 +
2/3 x
2/3 =
4/9
2/3