# Crowds

Contents

If you need to fill a scene with characters – a school of fish, a mob of monsters, or a cast of robots – you need to design a bunch of simple body parts that can be combined in different ways. Try making your own robot from parts – and share it!

Discover how combinations were used to design crowds of robots in "WALL-E." This lesson introduces the counting principle using tree diagrams and takes 30-45 minutes to complete.

In this lesson we construct snakes using permutations and develop a powerful counting tool: the binomial coefficient. This lesson takes 45-60 minutes to complete.