Look at the way numbers change if you make them 1 or 10 more or less.
When we make numbers 1 more or less, the unit digit changes.
When we make numbers 10 more or less, the tens digit changes.
Answer these.
Look at the which digits change.
Try making up some more of your own.
You could stick to tens and units – or even try hundreds, tens and units!
I wonder what happens when you make numbers 100 more or less…
What do you think ? 
