Correct Answer - Option 2 : 69.12 km/hr
Given:
Speed of Aman for 1/4th of total distance = 36 km/hr
Speed of Aman for 1/3rd of total distance = 72 km/hr
Formula:
Average Speed = Total Distance/Total time taken
Calculation:
Take LCM (3, 4) = 12
Let the total distance = 12x
⇒ 1/4th of total distance = ¼ × 12 = 3x
⇒ 1/3th of total distance = 1/3 × 12 = 4x
⇒ Remaining distance = 12x – (3x + 4x) = 5x
⇒ Average speed = 12x/[(3x/36) + (4x/72) + (5x/144)]
⇒ Average Speed = 12x/[(12x + 8x + 5x)/144] = (12 × 144)/25 = 69.12 km/hr
∴ The average speed of Aman is 69.12 km/hr