### Doodles

Draw a 'doodle' - a closed intersecting curve drawn without taking pencil from paper. What can you prove about the intersections?

### Russian Cubes

I want some cubes painted with three blue faces and three red faces. How many different cubes can be painted like that?

### Picture Story

Can you see how this picture illustrates the formula for the sum of the first six cube numbers?

# L-triominoes

##### Age 14 to 16 Challenge Level:

A triomino is a shape made from three squares. Here is an L-triomino:

Here is a size 2 L-triomino:

It can be tiled with four size 1 L-triominoes:

Can you work out how to use the tiling of a size 2 L-triomino to help you to tile a size 4 L-triomino? Click here for a hint.

Devise a convincing argument that you will be able to tile a size 8, 16, 32... $2^n$ L-triomino using size 1 L-triominoes.

How many size 1 L-triominoes would you need to tile a size 8... 16... 32... $2^n$ L-triomino?

What about odd sized L-triominoes? The diagram below shows the region which needs to be tiled to turn a size 1 L-triomino into a size 3 L-triomino.

Can you find a quick way of tiling the region, using combinations of the 'building blocks' below?

In the same way, can you find a way of adding to your size 3 tiling to tile a size 5? Then a size 7, 9, 11...? Click here for a hint.
Devise a convincing argument that you will be able to tile any odd sized L-triomino using size 1 L-triominoes.

Combine your ideas to produce a convincing argument that ANY size of L-triomino can be tiled.

Here is an interactive you could use to try out your ideas.