Two trains of the same length are running on parallel tracks in the same direction at 48 km/h & 36 km/h respectively . The faster train passed the other train in 81 seconds . What is the length (meters) of each train ?

270 meter

When trains are moving in same direction than , 

Relative Speed  = 48 km/h - 36 km/h = 12 km/h

to convert km/hr into m/sec

X km/hr  × \(\frac{5}{18}\) = Y m/sec 

Length of train = Speed × Time 

Length of Train  = 81 × 12 × \(\frac{5}{18}\) = 270 meter