Question

A car travels at a speed of 80 km/h during the first half of its running time and at 40 km/h during the other half. Find the average speed of the car.

Answer 1

Let the total running time = x hrs

Speed in the first half of its running time i.e., x/2 hrs = 80 km/h

∴ Distance covered in x/2 hrs = 80 x (x/2) =80x/2 = 40x km 

Speed in second half its running time = 40 km/h 

∴ Distance covered in x/2 hrs = 40 x (x/2) = 20x km 

Total distance = 40x + 20x = 60x km

Total time = x/2 + x/2 = x hrs

∴ Average speed  = Total distance /Time  = 60x/x =60 km/hr