An 80 metre long train crosses a 120 metre long platform in 20 seconds, what is the speed of the train per hour? ans:
Total distance= length of train + length of platform

I. e 80+120= 200 m but need in kmph so 0.2 km

Time = 20 second but need in hours so 20/(3600)= 1/(180)

Speed = distance / time = 0.2*180= 36 kmph