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Think of a Number Puzzles Worksheet

Maths tricks trick 6: Think of a number · Set 16 · 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 9 and then doubled it. I got 34. What was my number?
  2. 2.I thought of a number, added 9 and then doubled it. I got 36. What was my number?
  3. 3.I thought of a number, multiplied it by 4 and added 1. I got 9. What was my number?
  4. 4.I thought of a number, multiplied it by 2 and added 2. I got 12. What was my number?
  5. 5.Magic trick! Think of 3. Double it, add 4, halve it, then take away 3. What number do you get?
  6. 6.I thought of a number, added 2 and then doubled it. I got 32. What was my number?
  7. 7.I thought of a number, added 2 and then doubled it. I got 12. What was my number?
  8. 8.I thought of a number, multiplied it by 3 and added 7. I got 46. What was my number?
  9. 9.I thought of a number, added 5 and then doubled it. I got 46. What was my number?
  10. 10.I thought of a number, multiplied it by 2 and added 9. I got 23. What was my number?
  11. 11.Magic trick! Think of 16. Double it, add 12, halve it, then take away 16. What number do you get?
  12. 12.I thought of a number, added 1 and then doubled it. I got 26. What was my number?
  13. 13.I thought of a number, added 3 and then doubled it. I got 46. What was my number?
  14. 14.I thought of a number, added 6 and then doubled it. I got 30. What was my number?
  15. 15.Magic trick! Think of 16. Double it, add 16, halve it, then take away 16. What number do you get?
  16. 16.Magic trick! Think of 11. Double it, add 8, halve it, then take away 11. What number do you get?
  17. 17.Magic trick! Think of 15. Double it, add 10, halve it, then take away 15. What number do you get?
  18. 18.I thought of a number, multiplied it by 4 and added 1. I got 53. What was my number?
  19. 19.Magic trick! Think of 11. Double it, add 14, halve it, then take away 11. What number do you get?
  20. 20.I thought of a number, added 7 and then doubled it. I got 40. What was my number?
  21. 21.Magic trick! Think of 9. Double it, add 4, halve it, then take away 9. What number do you get?
  22. 22.I thought of a number, added 3 and then doubled it. I got 14. What was my number?
  23. 23.Magic trick! Think of 16. Double it, add 4, halve it, then take away 16. What number do you get?
  24. 24.Think of 6. Multiply it by 3, then add 6. What number do you end with?
  25. 25.I thought of a number, multiplied it by 4 and added 6. I got 30. What was my number?
  26. 26.Magic trick! Think of 15. Double it, add 16, halve it, then take away 15. What number do you get?
  27. 27.I thought of a number, multiplied it by 5 and added 3. I got 43. What was my number?
  28. 28.I thought of a number, multiplied it by 4 and added 3. I got 59. What was my number?
  29. 29.Think of 13. Multiply it by 2, then add 1. What number do you end with?
  30. 30.Magic trick! Think of 5. Double it, add 10, halve it, then take away 5. What number do you get?
  31. 31.Magic trick! Think of 10. Double it, add 6, halve it, then take away 10. What number do you get?
  32. 32.I thought of a number, multiplied it by 3 and added 4. I got 37. What was my number?
  33. 33.Think of 10. Multiply it by 4, then add 5. What number do you end with?
  34. 34.I thought of a number, multiplied it by 4 and added 4. I got 60. What was my number?
  35. 35.Think of 2. Multiply it by 5, then add 4. What number do you end with?
  36. 36.Magic trick! Think of 5. Double it, add 6, halve it, then take away 5. What number do you get?
  37. 37.I thought of a number, added 1 and then doubled it. I got 14. What was my number?
  38. 38.I thought of a number, multiplied it by 3 and added 7. I got 22. What was my number?
  39. 39.Magic trick! Think of 5. Double it, add 8, halve it, then take away 5. What number do you get?
  40. 40.I thought of a number, multiplied it by 3 and added 1. I got 31. What was my number?

Answer key

  1. 8
  2. 9
  3. 2
  4. 5
  5. 2
  6. 14
  7. 4
  8. 13
  9. 18
  10. 7
  11. 6
  12. 12
  13. 20
  14. 9
  15. 8
  16. 4
  17. 5
  18. 13
  19. 7
  20. 13
  21. 2
  22. 4
  23. 2
  24. 24
  25. 6
  26. 8
  27. 8
  28. 14
  29. 27
  30. 5
  31. 3
  32. 11
  33. 45
  34. 14
  35. 14
  36. 3
  37. 6
  38. 5
  39. 4
  40. 10

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