Example 1 · level 1
The table shows the number of books read in a month: 2 (frequency 7), 4 (frequency 4), 6 (frequency 7). Find the mean.
Show solution
- fx: 2 × 7 = 14, 4 × 4 = 16, 6 × 7 = 42.
- Σfx = 72, Σf = 18.
- Mean = 72 ÷ 18 = 4.
Answer: 4
CLASS 9 MATHS · STATISTICS
Mean of a frequency distribution
Mean = Σ(f × x) ÷ Σf: multiply each value by its frequency, add, and divide by the total frequency.
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Worked examples
Example 2 · level 2
The table shows the goals scored per match: 1 (frequency 4), 3 (frequency 5), 5 (frequency 5), 7 (frequency 3). Find the mean (to 2 decimal places).
Show solution
- fx: 1 × 4 = 4, 3 × 5 = 15, 5 × 5 = 25, 7 × 3 = 21.
- Σfx = 65, Σf = 17.
- Mean = 65 ÷ 17 = 3.82.
Answer: 3.8235
Example 3 · level 3
The table shows the marks (out of 100) scored by students in a test: 30 (frequency 9), 40 (frequency 4), 50 (frequency 7), 60 (frequency 2), 70 (frequency 5). Find the mean (to 2 decimal places).
Show solution
- fx: 30 × 9 = 270, 40 × 4 = 160, 50 × 7 = 350, 60 × 2 = 120, 70 × 5 = 350.
- Σfx = 1250, Σf = 27.
- Mean = 1250 ÷ 27 = 46.3.
Answer: 46.2963