Ungrouped data

A standard method from Measures of central tendency: the steps and worked examples.

Steps

Mean = sum ÷ number of items.
Median:
1. Put the data in order.
2. With n items, the median is the ((n + 1)/2)th item.
3. If n is even, take the mean of the two middle items.
Mode = the most frequent value (there can be more than one).

Example 1: Data: 3, 5, 5, 6, 8, 9, 13.

mean   = 49 ÷ 7 = 7
median = 4th item = 6
mode   = 5

Example 2: Grouped data.

Score	0–9	10–19	20–29	30–39
Class mark	4.5	14.5	24.5	34.5
Frequency	4	7	6	3

mean ≈ (4.5×4 + 14.5×7 + 24.5×6 + 34.5×3) ÷ 20
     = 370 ÷ 20
     = 18.5

For the whole topic, read Measures of central tendency: key points, common mistakes and how the DSE tests it.