Here is a subtraction: 52 − 17. Look at the units column first. We want to take 7 away from 2. Can we do it? What could we do when there are not enough units at the top to take away from?

The interactive works through three subtractions in columns, renaming a ten each time. Watch what happens to the tens and units digits when we rename, and check that the number is still worth the same.

Now we work through these three subtractions together on the board, one panel at a time: 45 − 19, then 63 − 28, then 81 − 79. Each one asks the same question first: are there enough units up top, or do we have to rename a ten? Say the answer aloud together before we fill in each column.

Today we work through these numbers together on the board: 38 − 15, then 52 − 27, then 70 − 34, and finally 91 − 58. Check the units column carefully before you decide whether you need to rename a ten.