Maths · Probability. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A combined event is made from two or more events, such as rolling two dice or taking two counters. List the outcomes in an ordered way with a sample space diagram, a tree diagram or a Venn diagram.
Two events are independent when one does not change the probability of the other. For A and B both to happen, multiply. Two events are mutually exclusive when they cannot happen together. For one or the other, add.
On a tree diagram, multiply along the branches and add the results of the routes you want. When an item is taken and not put back, both the number of that item and the total go down by one for the second pick.
Students find only one route when there are two. Exactly one of each, or different colours, can happen in two orders, for example red then blue and blue then red, and both must be added.
Answer: 8/15
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