Two trains each 250 m long are moving in opposite directions.  They cross each other in 15 seconds. If the speed of one train is 83 km/h, find the speed of the other train.

37 km/h

Total distance covered while crossing = 250 + 250 = 500 m

Time taken = 15 sec

Relative speed (S₁ + S₂) = $\frac{Total\;Distance}{time}$ = $\frac{500}{15}$ = $\frac{100}{3}$ m/sec

                                     = $\frac{100}{3}$ × $\frac{18}{5}$ km/hr = 120 km/hr

Speed of one train = 83 km/hr (given)

Speed of other train = 120 - 83 = 37 km/hr