MENTAL ARITHMETIC: SUBTRACTION
PROBLEMS
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Do the problem yourself first!
11. Explain why 41 − 35 = 6.
Because 35 plus 6 is 41.
12. Practice the following. Do not count on your fingers
| 2 + 7 = 9. | 1 + 5 = 6. | 2 + 3 = 5. | 2 + 6 = 8. | |||
| 3 + 4 = 7. | 5 + 4 = 9. | 3 + 2 = 5. | 1 + 7 = 8. | |||
| 5 + 3 = 8. | 1 + 4 = 5. | 5 + 2 = 7. | 6 + 3 = 9. | |||
| 4 + 3 = 7. | 4 + 5 = 9. | 2 + 2 = 4. | 3 + 3 = 6. | |||
| 1 + 8 = 9. | 1 + 5 = 6. | 1 + 2 = 3. | 3 + 5 = 8. | |||
13. Calculate each column mentally by adding to the smaller number.
| 8 − 5 = 3 | 90 − 60 = 30 | 95 − 40 = 55 | 43 − 20 = 23 | |||
| 80 − 50 = 30 | 80 − 30 = 50 | 63 − 10 = 53 | 78 − 20 = 58 | |||
| 825 − 500 = 325 | 84 − 30 = 54 | 62 − 30 = 32 | 94 − 30 = 64 | |||
| 95 − 70 = 25 | 72 − 50 = 22 | |||||
| 48 − 30 = 18 | 81 − 40 = 41 | |||||
| 99 − 20 = 79 | 66 − 50 = 16 | |||||
14. What number must you add?
| 8 + 6 = 14. | 8 + 5 = 13. | 7 + 9 = 16. | 8 + 3 = 11. | |||
| 2 + 9 = 11. | 4 + 8 = 12. | 9 + 8 = 17. | 7 + 6 = 13. | |||
| 5 + 7 = 12. | 9 + 7 = 16. | 6 + 5 = 11. | 5 + 6 = 11. | |||
| 6 + 9 = 15. | 5 + 9 = 14. | 5 + 8 = 13. | 8 + 9 = 17. | |||
| 9 + 4 = 13. | 6 + 6 = 12. | 8 + 7 = 15. | 6 + 8 = 14. | |||
| 7 + 5 = 12. | 4 + 9 = 13. | 9 + 3 = 12. | 4 + 7 = 11. | |||
| 3 + 8 = 11. | 7 + 8 = 15. | 9 + 2 = 11. | 8 + 4 = 12. | |||
| 6 + 7 = 13. | 7 + 4 = 11. | 9 + 5 = 14. | 3 + 9 = 12. | |||
15. What number must you add to the smaller number?
| 120 − 90 = 30 | 1900 − 1200 = 700 | |
| 126 − 90 = 36 | 1800 − 1400 = 400 | |
| 135 − 90 = 45 | 1842 − 1400 = 442 | |
| 124 − 80 = 44 | 1986 − 1600 = 386 | |
| 138 − 80 = 58 | 2004 − 1500 = 504 | |
| 146 − 80 = 66 | 2110 − 1700 = 410 | |
The complement to 10
| 6. | 3 + 7 = 10 | 9 + 1 = 10 | 4 + 6 = 10 | 2 + 8 = 10 | |||
| 1 + 9 = 10 | 8 + 2 = 10 | 6 + 4 = 10 | 5 + 5 = 10 | ||||
| 7 + 3 = 10 | |||||||
17. More complements to 10.
| 30 − 2 = 28 | 40 − 6 = 34 | 50 − 3 = 47 | 60 − 9 = 51 | |||
| 40 − 5 = 35 | 50 − 1 = 49 | 80 − 4 = 76 | 90 − 4 = 86 | |||
| 50 − 9 = 41 | 70 − 4 = 66 | 20 − 3 = 17 | 50 − 7 = 43 | |||
| 20 − 6 = 14 | 30 − 5 = 25 | 70 − 8 = 62 | 20 − 9 = 11 | |||
* * *
| 100 − 3 = 97 | 220 − 1 = 219 | |
| 100 − 7 = 93 | 350 − 3 = 347 | |
| 110 − 6 = 104 | 590 − 7 = 583 | |
| 120 − 8 = 112 | 600 − 5 = 595 | |
| 130 − 5 = 125 | 700 − 2 = 698 | |
18. Calculate mentally.
| $4.00 − 3¢ = $3.97 | $7.00 − 8¢ = $6.92 | $8.00 − 9¢ = $7.91 | ||
| $9.00 − 6¢ = $8.94 | $1.00 − 4¢ = $.96 | $6.00 − 7¢ = $5.93 | ||
19. Subtracting a one-digit number. Break off from the smaller
19. number the ones digit of the larger, and subtract. Then subtract the
19. rest of the smaller number.
Illustrate that in writing.
61 − 3 = 61 − 1 − 2 = 60 − 2 = 58
93 − 4 = 93 − 3 − 1 = 90 − 1 = 89
10. Calculate mentally.
| 22 − 3 = 19 | 61 − 2 = 59 | 71 − 4 = 67 | ||
| 53 − 4 = 49 | 83 − 5 = 78 | 22 − 4 = 18 | ||
| 31 − 3 = 28 | 62 − 5 = 57 | 91 − 2 = 89 | ||
| 21 − 4 = 17 | 42 − 3 = 39 | 92 − 4 = 88 | ||
| 43 − 5 = 38 | 72 − 4 = 68 | 52 − 5 = 47 | ||
| 73 − 4 = 69 | 24 − 5 = 19 | 44 − 5 = 39 | ||
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