Question

Abbas Travels a distance 120 km with a speed of 40 kilometre per hour and returns with a speed of 30 km per hour calculate the average speed for the entire train journey

Answer 1

total distance = 120 * 2 = 240 km (because, 120 is for one journey)
speed1 = 40km/h
speed2 = 30km/h

avg.speed = total distance/total time taken = ?

s1 = 40
d1 = 120km
t1 = d1/s1 = 120/40 = 3h

s2 = 30
d2 = 120km
t2 = d2/s2 = 120/30 = 4h

hence, avg.speed = total distance/total time taken = 240/(3+4)h = 240/7 =

34.2857 km/h


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Answer 2

total distance=240
total time taken by object to cover total distance=7 hours



now,
average speed=(total distance)/(total time)
=( (240)/(7) ) km/hour
=( (3.285714....) )km/hour