VIDEOS

Tree diagrams are used to show what happens in successive events (i.e. one after the other). They can be used for successive events which are independent or dependent, either way you still 'multiply through the tree diagram'. 

These first two videos shows you tree diagrams for independent events. This is often a question where an item is being selected then replaced and then selected again, so the probabilities on the first branch are the same as on the second branch:

These second two videos shows you tree diagrams for dependent events. This means the second branch is dependent on the first branch's outcome (this is conditional probability which you will see more of at A Level). Note this is often a question where an item is being selected and then NOT being replaced so the probabilities on the second branch are different to the first branch: