probability (+ tree diagrams)

IGCSE Maths Edexcel

P(A and B)

P(A) x P(B)

What are mutually exclusive events?

P(A or B) - they can’t happen at the same time

P(A or B)

P(A) + P(B)

What are independent events?

P(A and B) - the outcome of one doesn’t affect the other

P(event)

matching outcomes/total possible outcomes

Matching outcomes

1/total number of outcomes

Define sample space

All possible outcomes

Define theoretical probability

When we know the underlying probability of an event

Define relative frequency

How many times you got a certain outcome over how many times you ran the experiment

How do you form probability tree diagrams?

Have the probability of one event on one line, the probability of the other event on the other line - probability should add up to 1 - continue to break off ‘branches’ which should continue to add up to 1