The groundsman has to mark a circle of 10 m diameter on the playing field. He has a wooden peg and a ball of string. Describe how he does it

The groundsman can pound the stake into the ground. He can then, take the string and tie it loosely to the stake (making sure it can still turn around the stake), and measure the length to 5 feet, or the radius of the circle. The groundsman can then walk in a circle and mark it.