Solution:
Given:
1/3 part of journey is covered at the speed of = 18 km/h
1/4 part of journey is covered at the speed of = 27 km/h
And the remaining part of journey at the speed of = 45 km/h
Formula used:
Average Speed = Total Distance/Total Time
Calculation:
Let the total distance be S km
According to the question,
First part = S/3,
Time taken = (S/3)/18 = S/54
Second part = S/4
Time taken = (S/4)/27 = S/108
Remaining part = S - (S/3 + S/4) = 5S/12
Time taken = (5S/12)/45 = S/108
Total time = S/54 + S/108 + S/108 = 4S/108 = S/27
The Average speed = Total distance/Total time
Average Speed = S/(S/27) = 27
∴ The average speed of the whole journey will be 27 km/hr
