Robin travels one-fourth of the distance at 20 km/h, another one-fourth at 10 km/h, and the remaining distance at 80 km/h. Find Robin's average speed for the entire distance (correct to 2 decimal places).
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 22.86 km/h.
Average Speed = Total Distance/Total Time
Let the total distance be 4x.
According to question,
1/4th of distance = 4x/4 = x
Hence x km distance at 20km/hr and another x km distance at 10km/hr.
Remaining distance = 4x - x - x = 2x
2x km distance at 80km/h
Average speed = 4x/(x/20 + x/10 + 2x/80) = 4x(80)/14x = 22.86 km/hr