At the front of a long column of soldiers is a man regularly hitting a drum 50 times a minute. The soldiers are told to place their left foot down on the ground when they hear the drum beat. The column is so long that the soldiers at the back put down their left feet at the same time as the soldiers in the front put down their right feet.
What is the minimum length of the column of soldiers? [Speed of sound in air is 330m/s]

Answer:

27) B

50 beats per minute means after every 60/50 seconds (1.2 seconds), there is one beat.

When soldiers at front put down their right foot, the soldiers at the back put down their left foot.

Therefore, the beat is adjusted to 1 every 30/50 seconds (0.6 seconds).

Minimum distance = (30/50) x 330 = 198 m