The cost of levelling a circular field at 50 paise per square metre is Rs. 7700. The cost (in Rs.) of putting up a fence all round it at Rs. 1.20 per metre is $$\left( {{\text{Use }}\pi = \frac{{22}}{7}} \right)$$

$$\eqalign{ & {\text{According to the question,}} \cr & {\text{Area}} \times {\text{Rate}} = {\text{Expenditure}} \cr & \pi {r^2} \times \frac{1}{2} = {\text{Rs}}{\text{. }}7700 \cr & {r^2} = \frac{{7700 \times 7}}{{22}} \times 2 \cr & \boxed{r = 70} \cr & {\text{Perimeter}} = 2\pi r \cr & = 2 \times \frac{{22}}{7} \times 70 \cr & = 440{\text{ meter}} \cr & {\text{Expenditure}} = 440 \times 1.20 = {\text{Rs}}{\text{. }}528 \cr} $$