= 63 km/hour Alternative Method: By using alligation rule, Let, the average speed = x The ratio of speeds = 72 : 56 = 9 : 7 So, ratio of time taken = 7 : 9
72−x
x−56
=
9
7
504 - 7x = 9x - 504 16x = 1,008 x = 63 So, the average speed = 63 km/hour.