Question

A car travels 20 km at uniform speed of 40 km/h and next 20km at uniform speed of 60 km/h.calculate the average speed for the whole journey

Answer 1

Given,
total distance travelled=20 km
For the 1st case:
time taken=20/40 hr=1/2 hr
For the 2nd case:
time taken=20/60 hr=1/3 hr
Thus,total time taken=1/2+1/3 hr=5/6 hr
Hence,Average speed=total distance/total time
=40/(5/6) km/hr
=(40*6)/5 km/hr
=48 km/hr.

Answer 2

Hi !

d = distance
s = speed
t = time

Total distance traveled = 20 + 20 = 40 km

Time taken to travel 1st 20 km = d/s = 20/40 = 1/2 = 0.5 hour
Time taken  to travel next 20 km  = d/s = 20/60 = 0.33 hour

Total time taken = 0.5 + 0.33 = 0.83 hour

Average speed = Total distance traveled / total time taken
                         = 40/0.83
                         = 48.19
                         = 48.2 km/hr

Hope this helps you !