Question
Calculate the mean of the distribution given below using the short cut method.
| Marks | $11 - 20$ | $21 - 30$ | $31 - 40$ | $41 - 50$ | $51 - 60$ | $61 - 70$ | $71 - 80$ |
| No. of students | $2$ | $6$ | $10$ | $12$ | $9$ | $7$ | $4$ |
