Correct Answer - Option 1 : 12 km/hr
Given:
Speed through cycle = 8 kmph
Speed through bus = 15 kmph
Speed through bike = 20 kmph
Speed through rickshaw = 12 kmph
Formula used:
Speed = Distance/Time
Calculation:
LCM of 4 speeds = LCM (8, 12, 15, 20)
⇒ 4 × 2 × 5 × 3 = 120
⇒ Total distance covered = 120 × 4
⇒ Total distance covered = 480 km
⇒ Time taken to travel from home to bus station = 120/8
⇒ Time taken 1 = 15 hours
⇒ Time taken to travel from bus station to B = 120/15
⇒ Time taken 2 = 8 hours
⇒ Time taken to travel on bike = 120/20
⇒ Time taken to travel on bike = 6 hours
⇒ Time taken to travel on rickshaw = 120/12
⇒ Time taken to travel on rickshaw = 10 hours
⇒ Average speed = (Total distance/4)/(Total time/4) (∵ average speed = average distance/average time)
⇒ Avg. Speed = 480/(15 + 8 + 6 + 10)
⇒ Avg. Speed = 480/39
⇒ 480/39 ≈ 12 km/hr
∴ Required answer is 12 km/hr.