Here is a sum to look at: 27 + 18. When we add the units, 7 and 8, we get 15. But there is only one little box for the units answer, and 15 will not fit in one box. Hands up: when the units make ten or more, what do you think we should do with the extra ten?

Look at these column additions. Every sum starts on the right, with the units, and sometimes ten ones bundle into one ten that is carried left. Keep your eye on where that carried ten goes.

Now we work through some additions together, column by column on the board. Our first sum is 38 + 27. After that we will do 45 + 26, then 57 + 38, then 69 + 27, each one a little harder than the last. Everyone tracks each step on the board with us: for every sum we ask whether the units overflow and a ten must be carried, and we say each step aloud before we check it.

Today we work through these additions together, getting a little harder each time: 23 + 14, then 36 + 27, then 58 + 35, then 49 + 49. For each one we ask the same question first — did the units overflow, so do we carry?

What we learned

• When the units make ten or more, we write the units digit and carry a ten.
• The carried ten goes above the tens column, because ten ones make one whole ten.
• We always add the units first, then the tens with any carried ten included.