Tree diagrams are a visual way of showing all possible outcomes of two or more events. 

Each branch is a possible outcome and is labelled with probability. If a die was to be rolled twice, a tree diagram can show the probability of a 6 being rolled at each attempt. The tree diagram would look like the one below:



Question


A bag contains 4 blue counters and 3 red counters.




A box contains 5 blue counters and 2 red counters.





Complete a tree diagram and work out the probability of selecting two red counters.

Solution


You can see that the probability of RED on both occasions is: