Sarah and Mike conclude that it is wednesday. But five minutes later it is already friday. How is that possible?

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?

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?