Question

A train speeds past a pole in 15 sec and a platform 100 m long in 25 sec its length is

Answer 1

let the speed of the train be x,
and the length of train be y.
then,
 for crossing pole         =>    x = y/15             ......eq, (i)
 for crossing platform   =>    x = (y+100)/25            .......eq. (ii)

now,
putting the value of x from eq. (i) in (ii)
=> y/15 = (y+100)/25
=> y*5=(y+100)*3
=> 5y = 3y + 300
=> 2y = 300
=> y = 150

Hence, the length of the train is 150 m.