Let the length of the bridge be x metres and length of the first train at 90 km/hr be y metres. Then,
(x + y) = \(\bigg[\bigg(90\times\frac{5}{18}\times36\bigg)\bigg]\)m = 900 m
∴ The second train crosses the bridge by covering a distance of [x + (y – 100)] m at the rate of 45 km/hr or 12.5 m/s, i.e., 800 m at 12.5 m/s (∵ x + y = 900 m)
⇒ Time taken by the second train to cross the bridge = \(\frac{800}{12.5}\)sec = 64 seconds.
