A tree diagram can be used to show probabilities of events.
The diagram looks like the branches of a tree.
 The probability of each event should be marked on each branch.
 The probabilities on each set of branches must always add up to 1.
e.g. The tree diagram shows the probabilities when 2 coins are tossed. The coins are "fair" that is there is an equal probability that a "head" or a "tail" will be face up.
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From the diagram there are 4 possible outcomes:
Therefore the probability of each of these events occurring is (1 out of 4 possibilities).
This can also be calculated using the multiplication principle. e.g. P(H,H) =
Tree diagrams are useful for dealing with problems of games of chance.
One such game involves picking coloured balls from a bag. There are 8 balls in a bag, 5 of them are red and 3 of them green. If two balls are picked out at random and not replaced, what is the probability of getting two of the same colour?
Draw a tree diagram. The second selection is out of 7 because one ball has been removed. From the diagram: P(Two balls are same colour) = P(red, red) + P(green, green)
