Question

One third part of a certain journey is covered at the speed of 18 km/hr, one fourth part at the speed of 27 km/hr and the rest part at the speed of 45 km/hr. What will be the average speed for the whole journey?

• A. 35 km/hr
• B. 27 km/hr
• C. 24 km/hr
• D. 22 km/hr

Answer 1

Answer:

B. 27 km/hr

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