In this section, we will learn how to find the average speed.
What is round trip ?
Travelling in one direction at a certain rate of speed, and then returning along the same route at a different rate of speed is known as round trip.
Finding average speed :
If a person travels from A to B at some speed, say "x" miles per hour. He comes back from B to A at different speed, say "y" miles per hour. Both the ways, he covers the same distance, but at different speeds.
Then, the formula is to find the average speed for the whole journey is given below.
= 2xy / (x + y)
The purpose of finding the average speed :
For example, a car traveling from one city to another will rarely move at a constant speed. It is more likely that the car's speed will fluctuate during the trip.
The car might travel at 50 mph for some time and then slow down to 20 mph. It's possible that at certain times, the car is even at full stop (such as, at a red light). To calculate the car's average speed, we don't really care about the fluctuations in its speed.
We only care about the total distance traveled by the car and the elapsed time to cover that distance.
Examples Problems on Finding Average Speed of the Round Trip
Example 1 :
Mr Brown drove at a speed of 96 km/hr to his office every morning. He returned from work at the speed of 72 km/hr. What was his average speed for the round trip ?
Mr Brown covers the same distance. To find the average speed, we may use the formula
= 2xy / (x + y)
x = 96 km/hr and y = 72 km/hr
Average speed = 2(96) (72) / (96 + 72)
= 2 ⋅ 96 ⋅ 72 / 168
= 8 ⋅ 72 / 7
= 88 2/7 km/hr
Hence the average speed is 88 2/7 km/hr.
Example 2 :
Mr John drives at a constant speed of 108 km/h to his office every morning. He drives at a constant speed of 72 km/hr for his return trip. What is his average speed for the round trip ?
Mr John is covering the same distance.
x = 108 km/hr and y = 72 km/hr
Average speed = 2xy / (x + y)
= 2 ⋅ 108 ⋅ 72 / (108 + 72)
= 86.4 km/hr
Hence the average speed is 86.4 km/hr.
After having gone through the stuff given above, we hope that the students would have understood how to find the average speed of a round trip.
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