Correct Answer - Option 4 : 46.2 km / h
Given:
n first case:
Speed(S1) = 40 km/hr
Distance(D1) = 10 km
In second case:
Speed(S2) = 50 km/hr
Distance(D2) = 20 km
Formula:
Average Speed = (Total Distance/Total Time)
Time = Distance/Speed
Calculation:
Total Distance = 10 + 20 = 30 km
According to the question:
In first case:
Time = 10/40 = 1/4 hrs
In second case,
Time = 20/50 = 2/5
Total Time = 1/4 + 2/5 = (4 + 13)/20 = 13/20
Average Speed = (Total Distance/Total Time)
Average Speed = 30/(13/20) = 30 × 20/13 = 600/13 = 46.15 (46.2 approx)
∴ The average speed of whole journey is 46.2 km/hr.