A car travels three equal distances at the speed of 10 km/hr, 20 km/hr and 30 km/hr respectively. What is the average speed (in km/hr) for this journey?
Show answer & explanation
Correct answer: A
Explanation
Given:
Speed₁ = 10 km/h
Speed₂ = 20 km/h
Speed₃ = 30 km/h
According to the formula:
Average speed for equal distances = 3 / (1/v₁ + 1/v₂ + 1/v₃)
= 3 / (1/10 + 1/20 + 1/30)
= 3 / ((6 + 3 + 2)/60)
= 3 / (11/60)
= 3 × 60 / 11
= 180 / 11