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I think you will always get back to your original number, because adding 9 is the same as adding 10 and subtracting 1.
Digit Addition
Age 5 to 11
Challenge Level 
Digit Addition printable sheet
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?
What do you notice?
Try the trick again with a new starting number from 1 to 9. What do you notice now?
Will this always happen if you start with a number from 1 to 9?
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 is happening?
Can you explain the trick in a different way?
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