GCSE Maths: Statistics and Probability Revision Guide

Averages and spread

The mean is the total divided by the number of values. The median is the middle value when data is ordered. The mode is the most frequent value. Range is the difference between the highest and lowest values, showing how spread out the data is.

Representing data

Know how to read and draw common charts: bar charts, pie charts (where each slice's angle is a proportion of 360°), scatter graphs (showing correlation between two variables) and cumulative frequency graphs.

Probability basics

Probability is always between 0 (impossible) and 1 (certain). For equally likely outcomes, probability = number of favourable outcomes ÷ total number of outcomes. Probabilities of all possible outcomes for an event sum to 1.

Combined events

Use a sample space diagram or tree diagram for combined events. For independent events, multiply probabilities along the branches of a tree diagram; to find the probability of "either/or", add the relevant branches.

Common mistakes

• Confusing mean, median and mode — know exactly how to calculate each.
• Forgetting probabilities on a tree diagram for dependent events change after the first event.
• Reading values off a graph without checking the scale carefully.