### Construct-o-straws

Make a cube out of straws and have a go at this practical challenge.

### Matchsticks

Reasoning about the number of matches needed to build squares that share their sides.

How can the same pieces of the tangram make this bowl before and after it was chipped? Use the interactivity to try and work out what is going on!

# Tetrahedron Faces

### Why do this problem?

This problem offers opportunities for children to visualise a 3D shape. It also encourages conjectures and justifications.

### Possible approach

To begin with, encourage children to make conjectures about the number of different tetrahedra, asking pairs of children to come up with justifications for their ideas.

Having polydron available for children to make tetrahedra would be helpful. Alternatively, stickers could be stuck on ready-made tetrahedra. Children might also want to draw nets so isometric dotty paper would be useful.

### Key questions

Where could the other colours go?
Can you find another way?
How do you know the tetrahedra are different?
How will you record your tetrahedra?