http://www.ck12.org Chapter 1. Independent and Dependent Events
P(B) =probability of obtaining a sum less than 4P(B) =
3
36
Notice that there are 3 elements in common. Therefore, the events are mutually inclusive, and we must account for
the double counting.
P(AandB) =3
36
P(A∩B) =
3
36
P(A∩B) =
1
12
P(A∪B) =P(A)+P(B)−P(A∩B)
P(A∪B) =
15
36
+
3
36
−
1
12
P(A∪B) =
15
36
+
3
36
−
3
36
P(A∪B) =
15
36
P(A∪B) =
5
12
Points to Consider
- What is the difference between the probabilities calculated with the Multiplication Rule versus the Addition
Rule?