Question

A man covers 54kms at a speed of 9km/hr and the remaining 72 kms at 12km/hr what is his average speed for the whole journey

Answer 1

in 1st case time= 54/9=6hours
in second case time=72/12=6hours
average speed= total distance/total time
=(54+72)/6+6=126/12=10.5km/h

Answer 2

In The first case :
speed =distance/time
therefore 54/9kms = 6
In second case :
72/12kms = 6
Average speed = total distance / total speed
= (54+72)/(6+6)
= 126 / 12
= 1.5 km