Kevin, Charles, Larry and Alex are in a room that’s about 110 feet long. In front of them are 5 balls which are exactly 100 ft from the exit. The balls are yellow, purple, green, red and blue, respectively. Each man must carry a ball to the exit. After traveling 20 ft a ball will change color twice. The sequence of color changes is always the same: yellow, purple, green, red, and blue.
At 80 ft Kevin’s ball is red. At 40 ft Larry’s ball is purple. At 60 ft Charles’ ball is blue At 100 ft Alex’s ball is purple.
The remaining ball was blue. Here’s a table of each ball and the color it changes to at 20, 40, 60, 80 and 100 ft. Kevin’s started out yellow, Larry’s was green, Charles’ was red and Alex began with a purple ball, leaving blue as the one nobody picked.
Two guards were on duty outside a barracks. One faced up the road to watch for anyone approaching from the North. The other looked down the road to see if anyone approached from the South. Suddenly one of them said to the other, “Why are you smiling?”