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Adding and subtracting tens mentally

PROCEDURAL
Mathematics›Addition & Subtraction|Ages 6—7|ID: mt_I5j1ZWo2cn

Add and subtract a two-digit number and tens mentally and using concrete/pictorial representations

Mastery Evidence

  • Calculate 45 + 30 = 75 mentally
  • Calculate 82 − 40 = 42 mentally
  • Explain that only the tens digit changes when adding/subtracting tens

Assessment Prompt

“Can [child] quickly work out '54 + 30' or '78 − 20' in their head — knowing that only the tens digit changes?”

Curriculum Standards1 alignment

Maths/Y2/AS/5The national curriculum in England
Add and subtract two-digit numbers and tens

Add and subtract numbers using concrete objects, pictorial representations, and mentally, including a two-digit number and tens.

Mathematics · Key Stage 1

Prerequisites2

Show full prerequisite tree
  • 10 More or 10 Less hard

    Adding/subtracting tens builds on mentally finding 10 more or less

    • One More Each Time soft

      10 more/less generalises the concept of one more/one less to tens

      • How Many in Total? hard

        Understanding 'one more/one less' requires understanding that each number represents a quantity (cardinality)

        • One-to-one counting hard

          Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'

    • The two digits of a two-digit number hard

      Mentally finding 10 more/less requires understanding that the tens digit changes

      • A Ten Is Ten Ones hard

        Understanding tens and ones place value requires the concept of 10 as a bundle

        • The teen numbers hard

          Understanding 10 as a bundle builds on understanding teen numbers as 'a ten and some ones'

          • How Many in Total? hard

            Understanding tens-and-ones composition requires cardinality — knowing numbers represent quantities

            • One-to-one counting hard

              Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'

          • Reading and writing numbers to 20 hard

            Composing/decomposing teen numbers requires reading and writing those numerals

            • How Many in Total? hard

              Reading/writing numerals 0–20 requires understanding that numerals represent quantities (cardinality)

              • One-to-one counting hard

                Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'

            • Writing digits 0-9 hard

              Writing numerals requires the motor skill of forming digits 0-9 (taught in English handwriting)

      • The teen numbers hard

        General two-digit place value extends from understanding teen number composition

        • How Many in Total? hard

          Understanding tens-and-ones composition requires cardinality — knowing numbers represent quantities

          • One-to-one counting hard

            Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'

        • Reading and writing numbers to 20 hard

          Composing/decomposing teen numbers requires reading and writing those numerals

          • How Many in Total? hard

            Reading/writing numerals 0–20 requires understanding that numerals represent quantities (cardinality)

            • One-to-one counting hard

              Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'

          • Writing digits 0-9 hard

            Writing numerals requires the motor skill of forming digits 0-9 (taught in English handwriting)

  • The two digits of a two-digit number hard

    Adding/subtracting tens requires place value understanding

    • A Ten Is Ten Ones hard

      Understanding tens and ones place value requires the concept of 10 as a bundle

      • The teen numbers hard

        Understanding 10 as a bundle builds on understanding teen numbers as 'a ten and some ones'

        • How Many in Total? hard

          Understanding tens-and-ones composition requires cardinality — knowing numbers represent quantities

          • One-to-one counting hard

            Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'

        • Reading and writing numbers to 20 hard

          Composing/decomposing teen numbers requires reading and writing those numerals

          • How Many in Total? hard

            Reading/writing numerals 0–20 requires understanding that numerals represent quantities (cardinality)

            • One-to-one counting hard

              Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'

          • Writing digits 0-9 hard

            Writing numerals requires the motor skill of forming digits 0-9 (taught in English handwriting)

    • The teen numbers hard

      General two-digit place value extends from understanding teen number composition

      • How Many in Total? hard

        Understanding tens-and-ones composition requires cardinality — knowing numbers represent quantities

        • One-to-one counting hard

          Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'

      • Reading and writing numbers to 20 hard

        Composing/decomposing teen numbers requires reading and writing those numerals

        • How Many in Total? hard

          Reading/writing numerals 0–20 requires understanding that numerals represent quantities (cardinality)

          • One-to-one counting hard

            Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'

        • Writing digits 0-9 hard

          Writing numerals requires the motor skill of forming digits 0-9 (taught in English handwriting)

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