(52) To find the mean,we calculate the class marks $(x_i)$ and $f_i x_i$:
| Class interval | Number of students $(f_i)$ | Class mark $(x_i)$ | $f_i x_i$ |
| $10-25$ | $2$ | $17.5$ | $35.0$ |
| $25-40$ | $3$ | $32.5$ | $97.5$ |
| $40-55$ | $7$ | $47.5$ | $332.5$ |
| $55-70$ | $6$ | $62.5$ | $375.0$ |
| $70-85$ | $6$ | $77.5$ | $465.0$ |
| $85-100$ | $6$ | $92.5$ | $555.0$ |
| Total | $\Sigma f_i = 30$ | | $\Sigma f_i x_i = 1860.0$ |
Mean $\bar{x} = \frac{\Sigma f_i x_i}{\Sigma f_i} = \frac{1860}{30} = 62$.
For the mode,the maximum frequency is $7$,which corresponds to the modal class $40-55$.
Here,$l = 40$,$h = 15$,$f_1 = 7$,$f_0 = 3$,$f_2 = 6$.
Mode $= l + \left( \frac{f_1 - f_0}{2f_1 - f_0 - f_2} \right) \times h = 40 + \left( \frac{7 - 3}{14 - 3 - 6} \right) \times 15 = 40 + \left( \frac{4}{5} \right) \times 15 = 40 + 12 = 52$.
Interpretation: The maximum number of students obtained $52$ marks (mode),while on average,a student obtained $62$ marks (mean).