Question

the cost of paving a circular plot at the rate of rupees 20 per square metre is rupees 4435.20 find the cost of fencing the plot at the rate of rupees 5 per metre. {the answer is rupees 264}​

Answer 1

$area \: of \: circle \: = \frac{4435.20}{20} \\ area = 221.76 \\ area \: of \: circle = \pi {r}^{2} \\ 221.76 = \frac{22}{7} \times {r}^{2} \\ 221.76 \times7 = 22 {r}^{2} \\ {r }^{2} = \frac{221.76 \times 7}{22} \\ {r}^{2} = \frac{1552.32}{22} \\ {r}^{2} = 70.56 \\ r = \sqrt{70.56} \\ r = 8.4$

$circumference = 2\pi \times r \\ 2 \times \frac{22}{7} \times 8.4 \\ = 52.8 \\ total \: cost \: of \: fencing = 52.8 \times 5 \\ = 264rs$

this is your answer