A person covers
of a distance with the speed of = 10 km / hr
A person covers next
of a distance with the speed of = 20 km / hr
Rest distance covers with the speed of = 40 km / hr
Formula: Average speed = Total distance / total time
Calculation: Let total distance be 120 km
of total distance
=120×()=40 km
of total distance =
120×()=40 km
Remaining distance
=120−40−40=40 km
Time taken by person to cover 40 km distance with the speed of 10 km / hr = 40 / 10 = 4 hrs
Time taken by person to cover 40 km distance with the speed of 20 km / hr = 40 / 20 = 2 hrs
Time taken by person to cover 40 km distance with the speed of 40 km / hr = 40 / 40 = 1 hr
Total time =
4+2+1=7 hrs
∴ Average speed = 120/7 km/hr