A. 45 m
B. 50 m
C. 55 m
D. 60 m
Converting km/hr to m/sec
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 a metres and its speed by b m/sec
Then, a / [ b - (5/9) ] = 9 and a / [ b - (10/9) ] = 10
=> 9b - 5 = a and 10(9b - 10) = 9a
=> 9b - a = 5 and 90b - 9a = 100
=> On Solving, we get a = 50
=> Length of the train is 50 m