A car travels 100 km at a speed of 90 km/h and returns with a speed of 30 km/h. Calculate the average speed for the whole journey.
In the first case, car travels at a speed of 90 km/h for a distance of 100 km
t1 = 100/90 h
In the second case, car travels at a speed of 30 km/h for a distance of 100 km
t2 = 100/30 h
Total distance travelled = 200 km
= 100/90 + 100/30
59