MENTAL ARITHMETIC: SUBTRACTION

PROBLEMS

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

Continue on to the next section.

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