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Mental addition and subtraction strategies

Add and subtract by splitting numbers into tens and ones.

Practice + answer key · 2 pages

Worksheet settings12 questions · 2 columns · A4
Number range

Both starting numbers stay within the range. Sums may exceed its upper bound.

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mathsprig-1
Content ID
7a0892c3
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1 page
Mental addition and subtraction strategiesMental addition and subtraction strategies. Practice. Calculate 20 + 25. Calculate 31 − 17. Calculate 82 + 75. Calculate 84 − 63. Calculate 36 + 31. Calculate 87 − 58. Calculate 14 + 82. Calculate 58 − 51. Calculate 54 + 34. Calculate 92 − 68. Calculate 63 + 57. Calculate 44 − 10.Name __________________________Date _______________Mental addition and subtraction strategiesCalculate each answer. Try splitting the second number into parts.Worked exampleCalculate 64 − 19 mentally. → 45Split 19 into 10 + 9.1.Calculate 20 + 25.2.Calculate 31 − 17.3.Calculate 82 + 75.4.Calculate 84 − 63.5.Calculate 36 + 31.6.Calculate 87 − 58.7.Calculate 14 + 82.8.Calculate 58 − 51.9.Calculate 54 + 34.10.Calculate 92 − 68.11.Calculate 63 + 57.12.Calculate 44 − 10.MathSprig · mathsprig.site · support@mathsprig.sitePage 1 of 1mathsprig-1 · mathsprig-v1 · 7a0892c3
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Practice + answer key · 2 pages

Arithmetic

What you’ll practice

Add and subtract whole numbers by splitting the second number into tens and ones.

A calculation can be easier when you take it in smaller steps. Try adding or subtracting the tens first, then the ones, and compare your method with the on-page explanation.

How this skill works

For 38 + 27, add 20 first and then add 7. This keeps track of the value being added without needing a written column method.

For subtraction, subtract the tens contribution before the ones contribution. Check the final difference by adding back the whole subtracted amount.

Worked example

Calculate 64 − 19 mentally.
  1. Split 19 into 10 + 9.
  2. 64 − 10 = 54, then 54 − 9 = 45.
  3. Check: 45 + 19 = 64.

Answer: 45

Teaching notes

  • Write an intermediate value if it helps keep the steps clear.
  • The illustrated method is one valid strategy; a different correct mental method is also useful.
Practice questions
  1. Calculate 20 + 25.
  2. Calculate 31 − 17.
  3. Calculate 82 + 75.
  4. Calculate 84 − 63.
  5. Calculate 36 + 31.
  6. Calculate 87 − 58.
  7. Calculate 14 + 82.
  8. Calculate 58 − 51.
  9. Calculate 54 + 34.
  10. Calculate 92 − 68.
  11. Calculate 63 + 57.
  12. Calculate 44 − 10.
Answers and steps
  1. 45
    1. Split 25 into 20 + 5.
    2. Add in parts: 20 + 20 = 40, then 40 + 5 = 45.
  2. 14
    1. Split 17 into 10 + 7.
    2. Subtract in parts: 31 − 10 = 21, then 21 − 7 = 14.
  3. 157
    1. Split 75 into 70 + 5.
    2. Add in parts: 82 + 70 = 152, then 152 + 5 = 157.
  4. 21
    1. Split 63 into 60 + 3.
    2. Subtract in parts: 84 − 60 = 24, then 24 − 3 = 21.
  5. 67
    1. Split 31 into 30 + 1.
    2. Add in parts: 36 + 30 = 66, then 66 + 1 = 67.
  6. 29
    1. Split 58 into 50 + 8.
    2. Subtract in parts: 87 − 50 = 37, then 37 − 8 = 29.
  7. 96
    1. Split 82 into 80 + 2.
    2. Add in parts: 14 + 80 = 94, then 94 + 2 = 96.
  8. 7
    1. Split 51 into 50 + 1.
    2. Subtract in parts: 58 − 50 = 8, then 8 − 1 = 7.
  9. 88
    1. Split 34 into 30 + 4.
    2. Add in parts: 54 + 30 = 84, then 84 + 4 = 88.
  10. 24
    1. Split 68 into 60 + 8.
    2. Subtract in parts: 92 − 60 = 32, then 32 − 8 = 24.
  11. 120
    1. Split 57 into 50 + 7.
    2. Add in parts: 63 + 50 = 113, then 113 + 7 = 120.
  12. 34
    1. Split 10 into 10 + 0.
    2. Subtract in parts: 44 − 10 = 34, then 34 − 0 = 34.