Suppose you sit in a rubber boat in a swimming pool. In the boat lies a stone. You throw this stone from the boat into the pool. Will the water level in the pool raise or drop?

A bookworm eats a straight way through a encyclopedia consisting of ten parts. Each part has 1000 pages. The bookworm starts on the front cover of the first part and ends on the back cover of the last part. From how many pages did the bookworm eat?

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?