You have to determine a way to cut a circular cake into exactly three portions of equal size. The only marking on the cake is a candle in the very center.
All you have to work with is a knife that is at least as long as the diameter of the cake, and your hands. No other equipment is available..
Though this puzzle requires some understanding of geometry, it is also a practical problem. Use the knife as a way of making measurements and referencing dimensions
The knife doesn't need to be as long as the diameter of the cake, it could be as long as the radius and the same method would work!