Question

One fourth of a journey is covered at the rate of 50 km/h, one third at the rate of 60 km/h and the rest at the rate of 100 km/h. find the average speed for the whole journey.

Answer 1

suppose total distance = x km
x ka 1/4 = x/4 journey speed = 50km/h
time = distance / time = x/4/50= x/200 hour
x ka 1/3 = x/3 journey speed = 60km/h
time = x/3/60 = x/180 hours
3x+4x. 7x
total = x/4+x/3= ------ = ----------
12. 12

rest = X- 7x/12= 5x/12
5x/12 journey speed = 100km/h
time = 5x/12/100 = 5x/1200 = x/240 hours
total distance = x km
total time = x/200 + x/180 + x/240
36x + 40x + 30x. 106x
---------------------- = ----------- hour
7200. 7200
x. 7200x
average speed = -------------- = ---------- = 67.92
106x/7200. 106x
avg speed = 67.92km/h ans