| Number | 5 | 10 | 15 | 20 | 25 | 30 | 35 |
| Frequency | 1 | 2 | 5 | 6 | 3 | 2 | 1 |
Solution:
We write the numbers in cumulative frequency table.
| Marks (x) | No. of students (f) | Cumulative frequency | fx |
| 5 | 1 | 1 | 5 |
| 10 | 2 | 3 | 20 |
| 15 | 5 | 8 | 75 |
| 20 | 6 | 14 | 120 |
| 25 | 3 | 17 | 75 |
| 30 | 2 | 19 | 60 |
| 35 | 1 | 20 | 35 |
| Total | Ʃf = 20 | Ʃfx = 390 |
Mean = Ʃfx/Ʃf
= 390/20
= 19.5
Hence the mean is 19.5.
Here number of observations, n = 20 which is even.
So median = = ½ ( n/2 th term + ((n/2)+1)th term)
= ½ (20/2 th term + ((20/2)+1)th term)
= ½ (10 th term + (10+1)th term)
= ½ (10 th term + 11th term)
= ½ (20+20) [Since all observations from 9th to 14th are 20]
= ½ ×140
= 20
Hence the median is 20.