General Maths – Statistics Cheat Sheet
Key formulas, when to use them, and quick examples
1. Types of Data
• Categorical (qualitative): labels or groups (e.g. eye colour).
• Numerical (quantitative): numbers you can calculate with.
– Discrete: counted values (e.g. number of siblings).
– Continuous: measured values (e.g. height, weight).
2. Measures of Centre
Mean (average)
Formula: mean = (sum of all values) ÷ (number of values)
Example: Data = 2, 4, 6, 8
Mean = (2 + 4 + 6 + 8) ÷ 4 = 20 ÷ 4 = 5
Best used for: symmetric numerical data with no extreme outliers.
Median (middle value)
Steps:
1. Order the data from smallest to largest.
2. Pick the middle value.
If there are two middle values, average them.
Example: Data = 3, 5, 9, 12, 20 → Median = 9
Best used for: skewed data or when outliers are present.
Mode (most frequent value)
Example: Data = 2, 4, 4, 7, 9 → Mode = 4
Key formulas, when to use them, and quick examples
1. Types of Data
• Categorical (qualitative): labels or groups (e.g. eye colour).
• Numerical (quantitative): numbers you can calculate with.
– Discrete: counted values (e.g. number of siblings).
– Continuous: measured values (e.g. height, weight).
2. Measures of Centre
Mean (average)
Formula: mean = (sum of all values) ÷ (number of values)
Example: Data = 2, 4, 6, 8
Mean = (2 + 4 + 6 + 8) ÷ 4 = 20 ÷ 4 = 5
Best used for: symmetric numerical data with no extreme outliers.
Median (middle value)
Steps:
1. Order the data from smallest to largest.
2. Pick the middle value.
If there are two middle values, average them.
Example: Data = 3, 5, 9, 12, 20 → Median = 9
Best used for: skewed data or when outliers are present.
Mode (most frequent value)
Example: Data = 2, 4, 4, 7, 9 → Mode = 4
