For the following distribution:
| Marks | Number of students |
| Below 10 | 3 |
| Below 20 | 12 |
| Below 30 | 27 |
| Below 40 | 57 |
| Below 50 | 75 |
| Below 60 | 80 |
the modal class is 30 - 40.
Explanation:
| Marks | Number of students | Cumulative Frequency |
| Below 10 | 3 = 3 | 3 |
| Below 20 | (12 3) = 9 | 12 |
| Below 30 | (27 12) = 15 | 27 |
| Below 40 | (57 27) = 30 | 57 |
| Below 50 | (75 57) = 18 | 75 |
| Below 60 | (80 75) = 5 | 80 |
Here, we see that the highest frequency is 30, which **** in the interval 30 40.
