Simon takes two glasses, filled with equal amounts of milk and water each. He takes exactly one spoon of milk, pours it into the water and gives it a good stir. Then he takes exactly one spoon of the resulting mixture and pours that spoon in the milk. Question: what is more contaminated now, the milk or the water? (Thanks to everyone who took part and posted their answers on our YouTube channel and on Facebook! Please see the answer below!)

The answer: Let’s assume we’ve got 100 ml of liquid in each glass. And let’s assume a spoon is 10 ml. We first transfer 10 ml of milk into the water glass and give everything a good stir. In this glass now roughly one eleventh of the mixture is milk, hence the same ratio will be preserved in the spoon that pour back into the milk glass: it will contain 0,9 ml of milk and 9,1 ml of water. Which means that we end up with both glasses containing 100 ml each again, one with roughly 100 – 100/11 = 90,9 ml water and the second one with roughly 90 + 0,9 ml = 90,9 ml milk. The two liquids are equally contaminated!