If you can master Tree Diagrams you've got probability sorted!
Here's a diagram to help you understand them:
Here's an example:
A bag contains 6 red marbles and 4 blue marbles. A marble is drawn at random and not replaced. A second marble is then drawn.
Below is a tree diagram to show the probabilities, click on the question marks to reveal them:
The probabilities at the ends of the branches are found by multiplying the probabilities going across.
So to work out the probability of getting one marble of each colour, just add the ones we want going down:
The diagram below shows a tree diagram for the same question but this time there are 5 red balls and 3 green balls.
Click on the question marks to reveal the probabilities: