Add and subtract within 100 by applying related one-digit addition and subtraction facts: add and subtract any 2 two-digit numbers (2)

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Description

As for 2AS–3, Dienes and partitioning diagrams can be used to support pupils as they learn about strategies for carrying out these calculations.

To add 2 two-digit numbers, pupils need to combine one-digit addition facts with their understanding of two-digit place value. Pupils should first learn to add 2 multiples of ten and 2 ones before moving on to the addition of 2 two-digit numbers, for example:

  • 40 + 20 + 5 + 3 = 60 + 8 = 68
  • 40 + 5 + 20 + 3 = 60 + 8 = 68
  • 45 + 23 = 60 + 8 = 68

Language focus: “First I partition both numbers. Then I add the tens. Then I add the ones. Then I combine all of the tens and all of the ones.”

Pupils can then learn to be more efficient, by partitioning just one addend, for example:

45 + 23 = 45 + 20 + 3

= 65 + 3

When pupils learn to subtract one two-digit number from another, the progression is similar to that for addition. Pupils can first learn to subtract a multiple of ten and some ones from a two-digit number, and then connect this to the subtraction of one two-digit number from another.

There is an important difference compared to the addition strategy: pupils should not partition both two-digit numbers for subtraction as this can lead to errors, or calculations involving negative numbers, when bridging a multiple of 10, for example:

  • 63 – 17 60 – 10 + 7 – 3
  • 63 – 17 = 60 – 10 + 3 – 7

You can find out more about fluency and recording for addition and subtraction of two-digit numbers here in the calculation and fluency section: 2AS–4

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