R jogs at twice the speed of walking and runs at twice the speed of jogging. From his home to office, he covers half of the distance by walking and the rest by jogging. From his office to home, he covers half the distance jogging and the rest by running. What is his average speed (in km/h) in a complete round from his home to office and back home if the distance between his office and home is 10 km and he walks at the speed of 5 km/h?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e. 80/9.
Given:
Speed of walking = 5 km/h
Speed of jogging = Twice the speed of walking
Speed of running = twice the speed of jogging
Total distance from home to office = 10 km
Formula used:
Average speed = total distance/total time
Calculations:
Speed of jogging = 10 km/h
Speed of running = 20 km/h
Total distance = 10 + 10 = 20 km
Time taken from home to office = half distance by walking + half distance by jogging
⇒ 5/5 + 5/10 = 3/2
Time taken from office to home = half distance by jogging + half distance by running
⇒ 5/10 + 5/20 = 3/4
Total time = 3/2 + 3/4 = 9/4
Average speed = 20/(9/4) = 80/9