A man walks on a straight road from his home to a market 2.5 km away with a speed of 5 km/h. Finding the market closed, he instantly turns and walks back home with a speed of 7.5 km/h. If the total time of travel is 40 min find the average speed of the man for the whole journey.
From home to market, the time taken is time = dv=2.55=12hr =30 min.
He returns back with speed of 7.5 km/h in rest of time, that is, 10 minutes.
Distance = 7.5×1060=1.25km
Average speed = Total distanceTotal time