We’re back on to the idea of multiplying a whole number by ten, probably one of the most important concepts in primary maths. Of course, by now we all know that each digit moves one place to the left and a zero is placed in the units, acting as a place holder for the other digits. It is easy to say ‘add a nought’ but this just doesn’t work later when decimals are multiplied by 10 and it doesn’t help to explain dividing by ten, when each digit moves one place to the right. Children can do simple multiplication by ten quickly, but they do need to understand what is happening.