A particle covers 1/4^th  of the total distance at a speed of 20 km/hr, 1/2 of the total distance at a speed of 40 km/hr, 1/6^th of the total distance at a speed of 10 km/hr and remaining 1/12^th of the distance at a speed of 30 km/hr.  What is the average speed in km/hr?

The average speed of the particle is 22.5 km/hr.

Calculation details:

• The particle covers:
  • 1/4 of the distance at 20 km/hr,
  • 1/2 of the distance at 40 km/hr,
  • 1/6 of the distance at 10 km/hr,
  • 1/12 of the distance at 30 km/hr.
• Using formula: Average speed = total distance / total time.
• Total time is sum of (distance fraction / speed) for each portion.
• The calculated average speed is 22.5 km/hr.