Challenge Level

Here's a maths trick to try:

- Think of one of the numbers from 1 to 9.
- Add 9 to your number.
- Add the digits of your answer together. What is your new number?

Try the trick again with a new starting number. What do you notice now?

Jonas tried the trick with a few different numbers. He said:

I think you will always get back to your original number, because adding 9 is the same as adding 10 and subtracting 1.

Do you agree with Jonas? Can you help him explain what's happening?

Can you explain the trick in a different way?