DAY 220

TUNNEL VISION
(GAMES Magazine---Sam na Sam)

A train 125 yards long traveling at 40 miles per hour enters a long tunnel. Just as the last car is completely inside the tunnel, a man begins walking from the end of the train to the front. He walks at 5 miles per hour and reaches the front of the train just as it emerges from the tunnel into daylight. How long is the tunnel?

Answer:

The tunnel is 1,125 yards long. If x = the length of the tunnel, the man walks x yards at 45 miles per hour (the combined speed of the train and his walking). He walks this distance in the same time the train travels x - 125 yards at 40 miles per hour. Using the D = RT formula, since T is the same, x/45 = (x - 125) /40. This equation solves to x = 1,125.