Let speed in the return journey = V
∴ Speed in onward journey = (125/100) x V = 5V/4 km/h
Average speed = (2x 5V/4 x V) / (5V/4 + V) = 10V/9 km/h
∴ 1600 x (9/10V) = 30 [∴ halts for 2 h ]
∴ V = 1600 x 9/30 x 10 = 48 km/h
∴ Speed in onward journey = 5V/4 = 5/4 x 48 = 60 km/h