Probability

For equally likely outcomes the probability that something will happen is

Probability = number of successful outcomes / total number of possible outcomes

If you know the probability that an event will happen, you can calculate the probability that it won’t happen

Events are mutually exclusive if they can’t both happen at the same time

For mutually exclusive events

P( A or B ) = P(A) + P(B)

Events are independent if the outcome of one doesn’t affect the outcome of the other

For independent events

P(A and B) = P(A) X P(B)

A sample space diagram shows you all the possible outcomes of an event

Here are all the possible outcomes when two coins are flipped

For equally likely outcomes the probability that something will happen is

Probability = number of successful outcomes / total number of possible outcomes

If you know the probability that an event will happen, you can calculate the probability that it won’t happen

Events are mutually exclusive if they can’t both happen at the same time

For mutually exclusive events

P( A or B ) = P(A) + P(B)

Events are independent if the outcome of one doesn’t affect the outcome of the other

For independent events

P(A and B) = P(A) X P(B)

A sample space diagram shows you all the possible outcomes of an event

Here are all the possible outcomes when two coins are flipped