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How to Use a Tree Diagram

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Calculating Probabilities
How to Use a Tree Diagram

Now we read our diagram from left to write and do two things:

  1. Follow each path and write down the outcomes.
  2. Follow each path and multiply the probabilities.

Along the top path, we encounter heads and then heads again, or HH. We also multiply:
50% x 50% = (.50)x(.50)=.25=25%.
This means that the probability of tossing two heads is 25%.

We could then use the diagram to answer any question about probabilities involving two coins. As an example, what is the probability that we get a head and a tail? Since we were not given an order, either HT or TH are possible outcomes, with a total probability of 25%+25%=50%.

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