Question
Find the mean using the step deviation method.
| Class | 0-10 | 10-20 | 20-30 | 30-40 | 40-50 |
| Frequency | 6 | 10 | 15 | 9 | 10 |
✓
Answer
| Class | x | frequency(f) | $u=\frac{x-25}{10}$ | 𝑓u |
| 0-10 | 5 | 6 | -2 | -12 |
| 10-20 | 15 | 10 | -1 | -10 |
| 20-30 | 25 | 15 | 0 | 0 |
| 30-40 | 35 | 9 | 1 | 9 |
| 40-50 | 45 | 10 | 2 | 20 |
| $\sum f=50$ | $\sum f u=7$ |
= 26.4
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