Look at this number on the board: 305.

Each number-symbol, like the 3, the 0 or the 5, is called a digit.

Hands up: which digit do you think is worth the most in this number, and which one is worth the least? And that little zero sitting in the middle, what is it there for, could we just leave it out?

The interactive builds each number from place-value blocks: hundred-flats, ten-rods and single units. Watch what each column holds, including full columns and any that sit empty.

Today we build numbers together on the place-value mat with H, T and U columns. You will hear a number called out, then one of us will come up and build it: the right number of hundred-flats, ten-rods and units. The rest of us will check that every column matches.

Now we work through these numbers together at the board: 162, then 308, then 740, then 909. The zeros catch people out, so for each one we will all say it aloud and name the empty column together, then watch as the pupil at the board builds it and checks it.

What we learned today

• Where a digit sits decides what it is worth: hundreds, tens or units.
• Each column is ten times the one on its right: ten units make one ten, and ten tens make one hundred.
• A zero holds a column empty so the other digits stay in their right places.

Coming up

Next time we follow the same ten-times rule one step further and add a brand-new column on the left, so we can build numbers far bigger than 999.