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Adding 9, 19 and 99 Mental Maths Worksheet

Mental maths lesson 4: Add and take away 9, 19 and 99 · Set 504 · 40 questions
TalentJR

How to do it in your head (Round and adjust): Add 9, 19, 99: add 10, 20, 100, then take 1 away. Take away 9, 19, 99: take away 10, 20, 100, then add 1 back. Ask yourself: did I use too much or too little?

NameDateTime takenScore ___ / 40
  1. 1.665 + 99 =
  2. 2.31 + 9 =
  3. 3.61 − 19 =
  4. 4.69 + 9 =
  5. 5.23 + 9 =
  6. 6.44 − 19 =
  7. 7.185 + 99 =
  8. 8.67 + 19 =
  9. 9.61 − 29 =
  10. 10.653 − 99 =
  11. 11.232 − 99 =
  12. 12.62 − 29 =
  13. 13.41 + 29 =
  14. 14.33 + 9 =
  15. 15.74 − 29 =
  16. 16.60 + 19 =
  17. 17.306 − 99 =
  18. 18.50 + 9 =
  19. 19.23 − 19 =
  20. 20.28 + 9 =
  21. 21.20 + 9 =
  22. 22.48 − 19 =
  23. 23.26 + 29 =
  24. 24.41 + 9 =
  25. 25.32 + 19 =
  26. 26.50 − 19 =
  27. 27.40 + 9 =
  28. 28.31 + 19 =
  29. 29.52 + 9 =
  30. 30.770 − 99 =
  31. 31.306 + 99 =
  32. 32.711 − 99 =
  33. 33.47 − 19 =
  34. 34.55 + 9 =
  35. 35.58 − 9 =
  36. 36.57 + 19 =
  37. 37.722 + 99 =
  38. 38.63 + 29 =
  39. 39.22 − 9 =
  40. 40.77 + 9 =

Answer key

  1. 764
  2. 40
  3. 42
  4. 78
  5. 32
  6. 25
  7. 284
  8. 86
  9. 32
  10. 554
  11. 133
  12. 33
  13. 70
  14. 42
  15. 45
  16. 79
  17. 207
  18. 59
  19. 4
  20. 37
  21. 29
  22. 29
  23. 55
  24. 50
  25. 51
  26. 31
  27. 49
  28. 50
  29. 61
  30. 671
  31. 405
  32. 612
  33. 28
  34. 64
  35. 49
  36. 76
  37. 821
  38. 92
  39. 13
  40. 86

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