Solution:
Given, mean is 56.Frequencies(fi) | Mid-value(xi) | fi xi | |
0-20 | 16 | 10 | 160 |
20-40 | 11 | 30 | 330 |
40-60 | 25 | 50 | 1250 |
60-80 | P | 70 | 70p |
80-100 | 12 | 90 | 1080 |
100-120 | 10 | 110 | 1100 |
Total | 74+p |
| 3920+70p |
Since mean is 56,
Thus, p = 16.
Therefore, the correct option is 4.