Tree Diagrams

Tree diagrams

• You can use a tree diagram to answer questions involving conditional probability
• A tree diagram shows all the possible outcomes from a series of events and their probabilities
  • The outcome of the first event can sometimes affect the probability of the second
  • You can write the probability for each event on the branch
  • You multiply along the branches to find the probability of each outcome

Golden rules

• Look out for the words replace or put back in a probability question
  • With replacement = probabilities stay the same
  • Without replacement = first probability stays the same while the others change
• Multiply along the branches
• Add up the outcomes

Selection

• Selection can be without replacement
• The two events are not independent
• The probabilities for the second pick change depending on what is picked first