A train passes two bridges of length 800 m and 400 m in 100 seconds and 60 seconds respectively. The length of the train is:

Explanation:-

1^st Method:
Let length of the train be x m and speed of the train is s kmph.
Speed, s = ^(x+800)/₁₀₀ ..... (i)
Speed, s = ^(x+400)/₆₀ ..... (ii)
Equating equation (i) and (ii), we get,
Or, ^(x+800)/₁₀₀ = ^(x+400)/₆₀
Or, 5x+200 = 3x+2400;
Or, 2x = 400;
Or, x = 200 m.

2^nd Method:
As in both cases, the speed of the train is constant, and then we have;
Time α distance
¹⁰⁰/₆₀ = ^(x+800)/_(x+400);
Or, x = 200 m.