arithmetic - a train overtakes two persons who are walking in the same direction in which the train is going at the rate of 2 kmph and 4 kmph and passes them completely in 9 and 10 seconds respectively the length of the train is - skillgun

2 kmph = ( 2 x 5 /18) m/sec = 5/9 m/sec.
4 kmph = ( 4 x 5/18) m/sec = 10/9 m/sec.
Let the length of the train be x metres and its speed by y m/sec.
Then, ( x/ (y - 5/9) = 9 and ( x /(y - 10/9) = 10.
Therefore 9y - 5 = x and 10(9y - 10) = 9x
=> 9y - x = 5 and 90y - 9x = 100.
On solving, we get: x = 50.
Therefore Length of the train is 50 m.