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Column addition and subtraction

Level 1 · Ages 6–8

Quick recall· Let's wake up what you already know before we start.

Recall: 6 tens and 3 units, what number is that?

The whole lesson

Read it again any time, including while you work through the exercises.

Adding 34 and 25 in your head is fine. But 56 and 27? That gets trickier. Luckily, there is a magic method: setting out the sum in columns, with units under units and tens under tens.

To add, you always start with the units column, on the right. If the total goes past 9, for example 6 + 7 = 13, you write the 3 in the units and keep the extra ten for the next column: that is the famous carry. Imagine trading 10 loose marbles for 1 group of 10: nothing is lost, everything gets tidied up.

To subtract, same start: units first. Sometimes you hit a trap: 2 - 8, impossible! No panic: you break open a group of 10 to get 10 units back. The 2 becomes 12, and 12 - 8 = 4. In exchange, the tens column loses one group.

The secret to success: line up the digits carefully and never forget the carry. Take your time, column by column, and big numbers will hold no secrets for you.

The worked example, step by step

Set out and compute 56 + 27.

  1. 6 + 7 = 13

    I add the units: 13 is 3 units and 1 ten. I write 3 and carry 1.

  2. 5 + 2 + 1 = 8

    I add the tens without forgetting the carry: 5 + 2 + 1 = 8 tens.

Result: 56 + 27 = 83

Set out and compute 62 - 38.

  1. 2 - 8 : impossible

    I cannot take 8 units away when there are only 2. I break one ten of 62 to get 10 extra units.

  2. 12 - 8 = 4

    With 12 units, I can take away 8: 4 are left.

  3. 5 - 3 = 2

    The 6 in the tens became 5 (I broke one ten). That leaves 5 - 3 = 2 tens.

Result: 62 - 38 = 24