One-third of a journey is covered at the rate of 30 km/h, one-fourth at the rate of 50 km/h, and the rest at 60 km/h. Find the average speed for the whole journey. (Correct to 2 decimal places.)
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e.43.37 km/h
Given that
One-third of a journey is covered at a rate of 30 km/h
One fourth of a journey at the rate of 50 km/h and the rest at 60 km/h.
Formula used
Average speed = Total distance/Total time
Let total ditance is x km
Rest distance = x - (x/3 + x/4) = 5x/12
so, total time = (x/3)/30 + (x/4)/50 + (5x/12)/60
= x/90 + x/200 + x/144
According to the question
Average speed = x/(x/90 + x/200 + x/144) = 43.37 km/h