Conditional Probability

Probability

• If one event has already occured the probability of other events occurring might change
• This is called conditional probability
• The probability that an event X occurs given that an event Y has already occurred is written as P(X/Y)

Using venn diagrams

• You can solve some conditional probability problems using a Venn diagram
• If an event has already occured, then the sample space for the other events is restricted
• These venn diagrams show the outcomes of two events, A and B

Two-way tables

• You might have to work out probabilities from a two-way table
• This table shows how a group of students travel to school