On a particular evening a business man decides to work for some hours at his office in London because his wife gets out with her friends. After some hard work he opens the curtains of his office and looks outside (see the picture), but immediately he gets in panic. Why?

Suppose you have an infinite number of bricks and no cement or another material to connect the bricks to each other. You would like to build a tower like the one in the figure. How many bricks do you need in order to build a tower in which the highest brick is shifted three bricks with respect to the lowest brick?

There is something strange with the 5 euro note. What is it?