A man drive his car to the office at 20 km/hr.
After reaching office, he realize that its a new year holiday so he went back home at a speed of 30 km/hr.
Discounting the time spent in the stoppage what was his average speed of the journey ?
Answer is 24.
we can calculate it using Harmonic Mean
average speed = (2 x 20 x 30) / (20 + 30) = 1200 / 50 =24.
let distance between home and office is 20 km
then total distance =20+20=40km
total time = 1+2/3=5/3 hours
average speed =total distance/total time
average speed of car=(2*20*30)/50
v=s/t => v = 40km/(5/3)h => v = 24km/h
A cyclist covers his outward journey at 15 mph.
The return, over exactly the same distance, is uphill. He completes it at 5 mph.
What is the cyclist's average speed over the entire journey?
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It then returns to the first airport over exactly the same distance at an average speed of 144 miles per hour.
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Early one morning a family travelled to a shopping centre at 35 km/h.
After a day of Christmas shopping they returned, over exactly the same distance, at a crawl of only 14 km/h.
What was their average speed over the entire journey?
A coach covers its outward journey at 50 mph.
It returns, over exactly the same distance at 33.3333 mph.
What is the average speed of the coach over the entire journey?
A helicopter covers its outward journey at 330 mph.
It returns over exactly the same distance at 220 mph.
What is the helicopter's average speed over the entire journey?