For grouped data, use the midpoint of each class to estimate the mean: Σ(midpoint × frequency) ÷ Σfrequency. The answer is an estimate because we do not know the exact values.
The modal class has the highest frequency. The class containing the median is found by working out the median position and counting through the frequencies. Classes like 20 < m ≤ 40 include 40 but not 20.
Worked example
Classes 0–20 (10), 20–40 (15), 40–60 (5). Estimate the mean.
- Midpoints 10, 30, 50: 100 + 450 + 250 = 800.
- 800 ÷ 30 = 26.7 (1 d.p.).
Answer:about 26.7
Key words
- class
- a group of values
- midpoint
- the middle of a class
- estimate
- an approximate answer
Practise this
New questions every time.
Common Core-referenced: HSS-ID.A.2