A train 350 m long is running at the speed of 36 km/h. If it crosses a tunnel in 1 minute, the length of the tunnel in metres:

Answer: Option B

Let the length of the tunnel be x m
Time = $$\frac{\text{Length of train}+\text{Length of tunnel}}{\text{Speed}}$$
60 = $$\frac{350+\text{x}}{10}$$
$$\text{Speed}=\frac{36\times 5}{18}=10\text{m/sec}$$
x = 250 meters
Therefore length of tunnel is 250 meters