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:
Correct Answer: 200m
1st Method:Let length of the train be x m and speed of the train is s kmph.Speed, s = $$\frac{{x + 800}}{{100}}$$ . . . . . (i)Speed, s = $$\frac{{x + 400}}{{60}}$$ . . . . . (ii)Equating equation (i) and (ii), we get,Or, $$\frac{{x + 800}}{{100}}$$ = $$\frac{{x + 400}}{{60}}$$Or, 5x + 200 = 3x + 2400Or, 2x = 400Or, x = 200m2nd Method:As in both cases, the speed of the train is constant, and then we have;Time α distance$$\eqalign{ & \frac{{100}}{{60}} = \frac{{x + 800}}{{x + 400}} \cr & {\text{or,}}\,\,x = 200{\text{m}} \cr} $$