(A) 225 m
(B) 275 m
(C) 389 m
(D) 480 m
Correct Option is: D
Time taken to cross the bridge(12 km) = 600 seconds.
Speed of the train = Distance / Time
= 12/600 km/s
= 12000/600 m/s
= 20m/s
Train crosses a girl in 24 seconds.
Length of the train = Speed of the train x Time Taken
= (20 *24)m
= 480m
Hence the required length is 480 m.