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

Add or multiply

• 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)

Sample space diagrams

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

• Here are all the possible outcomes when two coins are flipped