A motorist travel to a place 150 km away at an avearge speed of 50 km/hr and…
2024
A motorist travel to a place 150 km away at an avearge speed of 50 km/hr and returns ar 30 km/hr.His average speed for the whole jouney in km/hr is
- A.
36.5 km/hr
- B.
37.5 km/hr
- C.
35.5 km/hr
- D.
34.5 km/hr
Attempted by 5 students.
Show answer & explanation
Correct answer: B
Step-by-Step Solution
When a motorist travels to a destination at one speed and returns over the same distance at a different speed, the average speed for the entire journey is the harmonic mean of the two speeds.
Identify the speeds:
Speed going (x) = 50 km/hr.
Speed returning (y) = 30 km/hr.
Apply the Average Speed Formula: For two equal distances, the formula for average speed is: Average Speed = (2 * x * y) / (x + y)
Calculate the value:
Average Speed = (2 * 50 * 30) / (50 + 30)
Average Speed = 3000 / 80
Average Speed = 37.5 km/hr.