Question

1. Two persons are walking in the same direction at speeds 4 km/hr and 8 km/hr. A train comes running from behind and passes them in 8 and 9 seconds respectively. The speed of the train is:

Answer 1

Assume the length of the train as D
x be the speed of the train

then.,
D/8=x-3
and
D/10= x-5

solving this 
8x-24 =10x-50
2x=26
x=13
ie.,speed of the train is 13km/hr