A rectangular field is 90m and 70m. A man walks round it at the rate of 4km per hr.What time will he take in making 4 rounds?

Given, length of rectangular field = 90 m 

and breadth = 70 m.

Distance covered by man in completing 1 round along the rectangular field = perimeter of  rectangular field

= 2(l + b) = 2 (90 m + 70 m) = 320 m

∴ distance covered by the man in completing 4 rounds = 4 × 320 m = 1280 m = 1.28 km

Also, speed with which man walks = 4 km/hr

Time taken by man in completing 4 rounds = Distance/speed

= 1.28/4

= 0.32 hour

= 0.32 × 60 minutes =  19.2 minutes