Question

1/3 of a certain journey is covered at the rate of 25 km/hr ,1/4at the rate of 30km/hr and rest of 50km/hr .what is the average speed for the whole journey?

Answer 1

d = total distance
t = total time
d/3 at 25
d/4 at 30
5d/12 at 50

t = (d/3)/25 + (d/4)/30 + (5d/12)/50
150t = 2d + 5d/4 + 5d/4 = 9d/2
300t = 9d
t = 3d/100
d = 100t/3
d/t = rate = 100/3
= 33 1/3 km/hr