| List-I (Method of weed control) | List-II (Measure of weed control) |
| (A) Preventive method of weed control | (I) Proper crop rotation |
| (B) Cultural method of weed control | (II) Control of Lantana camara (Prickly Pear) by Lantana bugs |
| (C) Chemical weed control | (III) Use of herbicide |
| (D) Biological weed control | (IV) Use of weed-free seeds |
Find the unknown frequency if 24 is the median of the following frequency distribution:
\[\begin{array}{|c|c|c|c|c|c|} \hline \text{Class-interval} & 0-10 & 10-20 & 20-30 & 30-40 & 40-50 \\ \hline \text{Frequency} & 5 & 25 & 25 & \text{$p$} & 7 \\ \hline \end{array}\]