Question

A bus travels ina distance of 120km with a speed of 40km/h and returns with a speed of 30km/h.Calculate the average speed for the entire journey.

Answer 1

In first case:

S1 = 120Km

V1 = 40Km/h

T1 = 120/40 = 3hr.

In second case:

S2 = 120km

V2 = 30km/h

T2 = 120/30 = 4hr

total time taken= 3+4=7hr

Total distance covered = 120+120 = 240km

Average speed = Total distance covered/Total time taken = 240/7=34.28Km/hr.

Hope it helps :-)

Answer 2

Average speed = total distance traveled (s) / total time taken (t)

total distance traveled(s)

= 120 km (for forward journey) + 120 km (for backward journey)

time for forward journey(t 1)

= 120 km / 40 km/hr

= 3 hr

time for backward journey (t 2)

= 120 km / 30 km / hr

= 4 hr

so, total time taken(t)

= t 1 + t 2

= 7 hr

so, average speed

= s/t = 240 km / 7 hr

= 34.286 km/hr