A train passes two persons walking in the same direction as the train. The time it takes to move past the man running at 30km/h is 8sec, whereas the time it takes to cross the other man running at 34km/h is 9sec. What is the speed of the train?
Let the speed of the train be v km/h. Length of the train calculated with the data for the first man = $(v - 30) × 8$. It should equal the length obtained from the data for the second man. So $(v - 30) × 8$ = $(v - 34) × 9$. Please note that we have not converted seconds to hours because that factor will ultimately cancel away. Solving for v we get 66km/h.