Question

A train travels 20 km at a uniform speed of 60 kmh and next 20 km at a uniform speed of 80 km h calculate its average speed

Answer 1

average speed =69.62 km/ h

Answer 2

Time consumed for 1st 20km = 20 km/60kmh = 1/3h
Time consumed for 2nd 20km = 20 km/80kmh = 1/4h

∴ Total time = 7/12
Total distance = 40km

∴A.Speed = Total displacement/Total time
                 =  40 ÷ 7/12 
                 = 68.57 km/h