Correct Answer - Option 2 : 24 km / hr
Given:
A man covers a certain distance at the speed of 20 km/hr
Half of the certain distance covers at the speed of 40 km/hr
Formula:
Average speed = (Total distance)/(Total time)
Calculation:
Let total distance be 80 km
Half of the distance = 80/2 = 40 km
Time taken by the man to cover 80 km distance at the speed of 20 km/hrs = 80/20 = 4 hrs
Time taken by the man to cover 40 km distance at the speed of 40 kmhrs = 40/40 = 1 hrs
Total distance = 80 + 40 = 120 km
Total time = 4 + 1 = 5 hrs
∴ Average speed = 120/5 = 24 km / hrs
