Question : Find the mean of the following data using the assumed mean method :
| Class | 0-5 | 5-10 | 10-15 | 15-20 | 20-25 |
| Frequency | 8 | 7 | 10 | 13 | 12 |
Doubt by CBSE
Solution :
| Class Intervals (CI) | Frequency (Fi) | xi | di=xi-a | fidi |
| 0-5 | 8 | 2.5 | -10 | -80 |
| 5-10 | 7 | 7.5 | -5 | -35 |
| 10-15 | 10 | 12.5 = a | 0 | 0 |
| 15-20 | 13 | 17.5 | 5 | 65 |
| 20-25 | 12 | 22.5 | 10 | 120 |
| Σfi=50 |
Σfidi=70 |
By Assumed Mean Method
x̄ = a + Σfixi/Σfi
x̄ = 12.5 + 70/50
x̄ = 12.5 + 7/5
x̄ = 12.5 + 1.4
x̄ = 13.9
Hence, the required mean of the data is 13.9.