A man runs round a circular field of radius 50m at the speed of 12 km/hr. What is the time taken by the man to take twenty rounds of the field?

speed = 12 km/h =  $12\times \frac{5}{18}=\frac{10}{3}m/s$ 

distance covered =  $20\times 2\times \frac{22}{7}\times 50=\frac{44000}{7}m$ 

time taken  = distance /speed =   $\frac{44000}{7}\times \frac{3}{10}sec=\frac{4400\times 3}{7}\times \frac{1}{60}min=\frac{220}{7}min$