Suppose you have an enormous long rope. You place this rope on the soil along the equator, such that the rope forms a circle around the earth. After you have finished this big job, you increase the length of the rope by one meter. How far from the soil do yo have to attach the rope to make again a circle around the equator? Assume that the earth is a perfect sphere, without mountains etc.

A sultan has 14 daughters. He decides to tell every night four of his daughtes a fairy tale, but in such a way that every night, there will be another combination of four daughters. How many nights will keep the sultan busy telling fairy tales?

How many different squares are located on a chess-board?