ABDUL WHILE DRIVING TO SCHOOL COMPUTES THE AVERAGE SPEED FOR HIS TRIP TO BE 20 KM/HOUR. ON HIS RETURN TRIP ALONG THE SAME ROUTE , THERE IS LESS TRAFFIC AND THE AVERAGE SPEED IS 30 KM/HOUR. WHAT IS THE AVERAGE SPEED FOR ABDUL'S TRIP?
Let the distance of the school from Abdu;l's home to school be s km
Let the time from home to school be t1
Let the time between return journey be t2
Therefore Average Speed = s / t1 = 20 km /hr so t1 = s / 20 hrs.
and similarly s / t2 = 30 km / hr so t2 = s / 30 hrs.
Total distance covered is s + s = 2s km.
Total time =(s / 20 + s/ 30 ) hrs
2s / s( 1 / 20 + 1 / 30) h
2 * 20 * 20 / 30 + 20
= 2 * 20 * 20 * 30 / 50
= 24 km /hr.
The average speed is 24 km .hr