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 t_{1}

Let the time between return journey be t_{2}

Therefore Average Speed = s / t_{1} = 20 km /hr so t_{1} = s / 20 hrs.

and similarly s / t_{2} = 30 km / hr so t_{2} = 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