Path rules
Each path of a tree diagram represents an outcome.
Example
This tree diagram has 4 paths and each represents an outcome of the two-step experiment.
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Tip
The sum of the probabilities of all branches of a branch point must always be 1.
1st path rule: Multiplication rule
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Remember
Die probability of an outcome (or path probability) corresponds to the product of all probabilities along the path.
Example
(See picture above)Probability for 2 times red: $P(R, R)=\frac34\cdot\frac34=\frac{9}{16}$
Probability for first blue and then red: $P(B, R)=\frac14\cdot\frac34=\frac{3}{16}$