effataraI came up with the same answer but with a different logic.
1) The Time that one passenger is inside the tunnel = time taken by that one passenger to cross the tunnel = 5/30 = 1/6 = 10 mins
2) The Time that all the passengers are inside the tunnel = time taken by the train to cross the tunnel AFTER the moment the entire train is inside the tunnel.
So the distance that the train has to cover = 5000m - 500m = 4500m
So, time taken = 4500 / (30,000/60) = 9 mins
Hence the difference is 1 min. Ans A.
Bunuel,
VeritasKarishma, please let us know the logic behind each of our approaches.