You are in the middle of a circular lake. At the edge is a tiger.
In this puzzle, the tiger can't swim (which is funny, because when I was looking for a tiger photo, I found pictures of tigers doing just that). Instead, the tiger will run along the edge of the lake, doing its best to catch you. The tiger runs four times as fast as you can swim.
You want to get out of the lake, but if the tiger is waiting for you when you reach the shore, then the tiger will seriously damage your ability to not die. Can you get out of the lake safely? How?
This puzzle is a classic, not original.
See the solution