In this unforgettable scene from “My Left Foot,” Christy Brown’s siblings are doing maths. “What’s 25% of a quarter? That’s stupid. You can’t have a quarter of a quarter,” says his father. Christy tries to write something on his slate, but they can’t make sense of it. He can’t quite form the six properly, but it’s the right answer, 1/16.

### The Golden Ratio Nautilus

The nautilus shell is typically associated with the golden ratio. There is a dispute over whether the golden ratio nautilus is real or myth!