Multiple choice

A person travels a distance of 300 km and then returns to the starting point. The time taken by him for the outward journey is 5 hours more than the time taken for the return journey. If he returns at a speed of 10 km/h more than the speed of going, what is the average speed (in km/h ) for the entire journey?

  1. 15

  2. 24

  3. 20

  4. 30

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let outward speed = v and time = t. Then vt = 300 and (v+10)(t-5) = 300. Solving: v = 20 km/h (t=15h), return speed = 30 km/h (t=10h). Average speed = total distance/total time = 600/25 = 24 km/h. Average speed for equal distances is harmonic mean, not arithmetic mean.