How to add two-digit numbers in your head

For ages 5 to 8 (Years 1 to 3) · 2-minute read · free worksheet

Partitioning means splitting numbers into tens and ones. It is how schools teach mental addition, and it avoids writing the sum out.

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Worksheet includes an answer key for grown-ups

How it works

  1. Split both numbers into tens and ones.
  2. Add the tens.
  3. Add the ones.
  4. Put the two answers together.

Worked example

44 + 15: tens 40 + 10 = 50, ones 4 + 5 = 9. So 44 + 15 = 59.

Top tip

If the ones make more than 9, just add on: 29 + 13 is 30 + 12 = 42.
How to add two-digit numbers in your head: 44 + 15 = ? Tens 50, ones 9, answer 59

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