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Think of a Number Puzzles Worksheet

Maths tricks trick 6: Think of a number · Set 81 · 40 questions
TalentJR

The trick (Undo the steps): Going forwards: do the steps in order. Going backwards: start from the result and undo each step, last one first. Undo + with −, × with ÷, and doubling with halving.

NameDateTime takenScore ___ / 40
  1. 1.I thought of a number, added 2 and then doubled it. I got 12. What was my number?
  2. 2.Magic trick! Think of 9. Double it, add 10, halve it, then take away 9. What number do you get?
  3. 3.Magic trick! Think of 2. Double it, add 6, halve it, then take away 2. What number do you get?
  4. 4.I thought of a number, added 6 and then doubled it. I got 52. What was my number?
  5. 5.Magic trick! Think of 14. Double it, add 16, halve it, then take away 14. What number do you get?
  6. 6.Think of 3. Multiply it by 5, then add 2. What number do you end with?
  7. 7.Think of 11. Multiply it by 4, then add 8. What number do you end with?
  8. 8.I thought of a number, added 6 and then doubled it. I got 28. What was my number?
  9. 9.Magic trick! Think of 20. Double it, add 14, halve it, then take away 20. What number do you get?
  10. 10.I thought of a number, added 4 and then doubled it. I got 40. What was my number?
  11. 11.I thought of a number, added 2 and then doubled it. I got 44. What was my number?
  12. 12.Magic trick! Think of 19. Double it, add 4, halve it, then take away 19. What number do you get?
  13. 13.I thought of a number, added 1 and then doubled it. I got 8. What was my number?
  14. 14.I thought of a number, multiplied it by 2 and added 7. I got 27. What was my number?
  15. 15.Magic trick! Think of 3. Double it, add 4, halve it, then take away 3. What number do you get?
  16. 16.Think of 4. Multiply it by 4, then add 5. What number do you end with?
  17. 17.I thought of a number, multiplied it by 5 and added 2. I got 27. What was my number?
  18. 18.Magic trick! Think of 15. Double it, add 14, halve it, then take away 15. What number do you get?
  19. 19.I thought of a number, added 8 and then doubled it. I got 56. What was my number?
  20. 20.Think of 8. Multiply it by 5, then add 9. What number do you end with?
  21. 21.I thought of a number, multiplied it by 3 and added 5. I got 44. What was my number?
  22. 22.Magic trick! Think of 8. Double it, add 16, halve it, then take away 8. What number do you get?
  23. 23.Magic trick! Think of 19. Double it, add 16, halve it, then take away 19. What number do you get?
  24. 24.Think of 2. Multiply it by 4, then add 1. What number do you end with?
  25. 25.Magic trick! Think of 7. Double it, add 12, halve it, then take away 7. What number do you get?
  26. 26.I thought of a number, multiplied it by 2 and added 1. I got 11. What was my number?
  27. 27.I thought of a number, added 9 and then doubled it. I got 26. What was my number?
  28. 28.I thought of a number, added 1 and then doubled it. I got 30. What was my number?
  29. 29.Magic trick! Think of 15. Double it, add 12, halve it, then take away 15. What number do you get?
  30. 30.Magic trick! Think of 4. Double it, add 14, halve it, then take away 4. What number do you get?
  31. 31.I thought of a number, added 4 and then doubled it. I got 30. What was my number?
  32. 32.I thought of a number, added 8 and then doubled it. I got 32. What was my number?
  33. 33.Magic trick! Think of 12. Double it, add 16, halve it, then take away 12. What number do you get?
  34. 34.Magic trick! Think of 11. Double it, add 16, halve it, then take away 11. What number do you get?
  35. 35.I thought of a number, multiplied it by 5 and added 1. I got 71. What was my number?
  36. 36.Think of 4. Multiply it by 4, then add 1. What number do you end with?
  37. 37.Magic trick! Think of 15. Double it, add 18, halve it, then take away 15. What number do you get?
  38. 38.Magic trick! Think of 7. Double it, add 16, halve it, then take away 7. What number do you get?
  39. 39.I thought of a number, added 8 and then doubled it. I got 54. What was my number?
  40. 40.Magic trick! Think of 10. Double it, add 8, halve it, then take away 10. What number do you get?

Answer key

  1. 4
  2. 5
  3. 3
  4. 20
  5. 8
  6. 17
  7. 52
  8. 8
  9. 7
  10. 16
  11. 20
  12. 2
  13. 3
  14. 10
  15. 2
  16. 21
  17. 5
  18. 7
  19. 20
  20. 49
  21. 13
  22. 8
  23. 8
  24. 9
  25. 6
  26. 5
  27. 4
  28. 14
  29. 6
  30. 7
  31. 11
  32. 8
  33. 8
  34. 8
  35. 14
  36. 17
  37. 9
  38. 8
  39. 19
  40. 4

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