Mon Prof Augmenté
Branches of a Probability Tree
Age 18 Maths
A probability tree starts at one point and splits into branches, and each branch carries the chance of that single step. Multiply the fractions along a path to get the chance of the outcome sitting at its end.
Step by step
- Badge 1 sits on the head of the left brass peg, the single starting point every ribbon leaves from.
- Badge 2 sits on the copper tag clipped to the upper first ribbon, which carries that branch's chance of 1/2.
- Badge 3 sits on the head of the smaller peg where the upper ribbon splits a second time.
- Badge 4 sits on the top ivory card with two black discs, one finished outcome at the end of a path.
Examples
- Flip a coin twice: each of the four paths is 1/2 x 1/2 = 1/4.
- Two traffic lights on the way home: green then red is one path through the tree.
Key takeaways
- The branches leaving one point have probabilities that add to 1.
- Multiply along a path; add across paths that give the same outcome.
A quiz goes with this lesson
Three questions asked a few days later, to check the idea stuck — not that the picture was seen. In the app, with a subscription.