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1. 1. Addition & Subtraction of Decimals <ul><li>by </li></ul><ul><li>Doug McFarland </li></ul><ul><li>Horizon Academy </li></ul><ul><li>Roeland Park, Kansas </li></ul><ul><li>www.horizon-academy.com </li></ul>
2. 2. Add and Subtract like Columns 71 + 58 + 25 = _______ 4 1 15 RULE: Only add and subtract LIKE columns. 71 58 25 + tens ones
3. 3. 7.1 + 5.8 + 2.5 = _______ Add & Subtract like Columns . 4 1 15 RULE: Only add and subtract LIKE columns. 7 . 1 5 . 8 2 . 5 + ones ten ths
4. 4. The “Understood” Decimal <ul><li>Consider the whole number 15 </li></ul><ul><li>15 = 1 ten + 5 ones (10 + 5). </li></ul><ul><li>We could put a decimal to separate the whole number from the decimal. </li></ul><ul><li>15.0 There is NO value in the tenths column, so we put 0 (zero). </li></ul>
5. 5. Addition with the “Understood” Decimal <ul><li>If you were adding 15 + 12 you could write the problem 15.0 + 12.0 </li></ul><ul><li>15.0 + 12.0 = 27.0 or 27 </li></ul><ul><li>When there is no decimal value, the zero and the decimal are NOT written, but they are understood to still be there. </li></ul>
6. 6. Make The Columns Even <ul><li>34.5 + 21 + 8.5 </li></ul>.0 34.5 21. 0 8.5 + RULE: Add zeros to even the columns 34.5 21 8.5 +
7. 7. Make The Columns Even <ul><li>44.589 + 7.23 + 5 </li></ul>56.819 1 1 7 23 0 5 000 3 decimal columns 2 decimal columns 0 decimal columns 44.589 . . +
8. 8. Subtracting Decimals <ul><li>Remember how to even your columns. </li></ul><ul><li>Remember the “understood” . 0 when looking at a whole number like 7 </li></ul><ul><li>It could be 7. 0 or 7. 00 if needed . </li></ul><ul><li>In subtraction, it will be needed . </li></ul>
9. 9. Let’s Look at Subtraction <ul><li>34 – 12 = _____ </li></ul>34 - 12 22 tens ones
10. 10. Subtract Similar Columns <ul><li>34 – 1 . 2 = _____ </li></ul>RULE: Only add and subtract LIKE columns. 3 4 - 1.2 2.2 ones ones ten ths tens Warning ! !
11. 11. Subtract Similar Columns <ul><li>34 – 1.2 = _____ </li></ul>1 8 2 3 34. 0 - 1. 2 . ones ten ths 3 33
12. 12. Here’s a Tricky One <ul><li>8 - 3.56 = _______ </li></ul>.00 5.56 1 1 4. 4 4 8 - 3.56 8. 0 0 - 3. 5 6 7 9
13. 13. We’re Done! <ul><li>Nice job following along in the lesson! </li></ul><ul><li>Try to use what you learned in your work! </li></ul><ul><li>Doug McFarland ©2006 </li></ul>