If a boat goes a certain distance at 30 km/h and comes back the same distance at 20 km/hr, what is the average speed (in km/hr) for the total journey ?
24
For equal distances at two speeds, the average speed is the harmonic mean:
\[\bar v = \frac{2 v_1 v_2}{v_1+v_2} = \frac{2\times 30\times 20}{30+20} = \frac{1200}{50}=24 \text{ km/h}\]
Therefore the average speed is 24 km/h, not the arithmetic mean 25.
Similar Questions
To cover a distance of 144 km in 3.2 hours what should be the average speed of the car in meters/second?
Akhil rides first 12 km at a speed of 16 km/h and further 6 km at a speed of 20 km/h. Find his average speed (in km/h).
A train without stoppage travels with an average speed of 70 km/h, and with stoppage, it travels with the average speed of 56 km/h. How many minutes, does the train stop on an average per hour?
After excluding stoppages, the speed of a bus is 60 kmph and after including stoppages, it is 45 kmph. For how many minutes does the bus stop per hour?
Shyam drives his car 30 km at a speed of 45 km/h and, for the next 1 h 20 m, he drives it at a speed of 51 km/h. Find his average speed (in km/h) for the entire journey.
A car travels from A to B with 40 Km/h and returns from B to A with 60 Km/h. Its average speed during the whole journey is
A bus travels 150 Km in 3 hours and then travel next 2 hours at 60 Km/hr. Then the average speed of the bus will be
The distance between two stations, A and B, is 428 km. a train starts from station ‘A’ at 6:00 a.m and moves towards station ‘B’ at an average speed of 48 km/h. Another train starts from station ‘B’ at 6:20 a.m and moves towards statin ‘A’ at an average speed of 55 km/h. At what time will the trains meet?
X and Y travel a distance of 90 km each such that the speed of Y is greater than that of X. The sum of their speeds is 100 km/h and the total time taken by both is 3 hours 45 minutes. The ratio of the speed of X to that of Y is:
To cover a distance of 81 km in 1.5 hours what should be the average speed of the car in meters/second?
Important Questions from Average Speed
A person covers a certain distance at the speed of 60 kmph and returns to the starting point at a speed of 40 kmph . Find the average speed (in km/hour) of the person for the whole journey.
Kapil travels for 4.5 hours at a speed of 50 km / h and 7.5 hours at a speed of 70 km / h. At the end of it, he finds that he covered only 6/7 of the total distance. At what average speed should he travel so that the remaining distance traveled in 5 hours?
A car has to cover 125 kms in 5 hours. What will be the average speed of the car if it has covered 90 kms in the first 3 hours?
A scooter from P to Q travels at 40 km/h and from Q to P at 30 km/h. What is the average speed of the scooter?
A car covers a distance of 100 km at a speed of 60 km/h and another 200 km at a speed of 75 km/h, what is the average speed of the car in km/h for the whole journey? (correct to one decimal place)
