There are a lot of challenges you can set with this simple structure and set of rules.

The basic rules are:

- Each number must be the sum of the 2 numbers below it
- You can only use a number once

Here’s an example of one of the basic rules:

Here’s two examples of completed number triangles. But something’s wrong. What are the problems in each?

## Challenges

- What’s the lowest possible number that you can get in the top circle?
- Can you fill it with only odd numbers? If so, do it. If not, say why not.
- The number in the top is always bigger than the sum of numbers in the bottom row. Why is that?
- Can you get the number 10 in the top circle. How many different ways can you do it?
- Instead of the numbers, just put in if it’s odd or even and see how many different odd/even patterns you can come up with.

To try these at home or in class, download the activity pack (or just draw your own on paper)