A train takes 11 sec and 10 sec to cross two men who are walking in same direction at the speed of 5 km/hr and 4 km/hr respectively. Find speed of the train .

15 km/hr

Distance = Speed  ×  Time 

Let speed of train = a km/hr

When train and the man with speed 5 km/hr move in same direction

Relative speed = ( a - 5 ) km/hr

Distance = ( a - 5 ) × 10       ---------- ( 1 ) 

When train and the man with speed 4 km/hr move in opposite direction

Relative speed = ( a - 4 ) km/hr

Distance  =  ( a - 4 ) × 5    ------------- ( 2 ) 

Distance is same . so put equation 1 and 2 equal 

( a - 5 ) × 11  =  ( a - 4 ) × 10 

11a - 55 = 10a - 40 

a = 15 km/hr