Tree Diagrams Are Helpful!

Figuring out probabilities can be hard. Sometimes you add, sometimes you multiply, and it can get confusing. Tree Diagrams are here to help!

Here is a tree diagram for the toss of a coin:

There are two "branches" (Heads and Tails) The probability of each branch is written on the branch (usually in fraction form) The outcome is written at the end of the branch

We can extend the tree diagram to tossing a coin twice:






How do we calculate the overall probabilities?

• We multiply probabilities along the branches
• We add probabilities down columns

So there you go, when in doubt draw a tree diagram, multiply along the branches and add the columns. Make sure all probabilities add to 1 and you are good to go.

If you are still a little confused, visit mathisfun.com to see another helpful example.