A spinning disc is painted black on one half and white on the other (i.e., the line forming the border between the black and white regions of the disc is a diameter of the disc). The disk is spinning on a turntable in an unknown direction at an unknown speed. You have special video cameras that can observe the color of a single point on the disc. How many cameras do you need to determine the direction the disc is spinning?
How to Divide 8 Gold Coins between 2 farmers?