Decimals Class 2 Decimal Operations Addition Subtraction of
Decimals Class #2 Decimal Operations Addition & Subtraction of Decimal Numbers, Multiplication & Division of Decimal Numbers According to TASC, no calculators for these.
Adding decimals is much like adding whole numbers. The “trick” is to make sure you have lined up the place value columns correctly (KEEP THE DECIMALS IN 1 COLUMN). Example add: 0. 3 7 1 3. 5 + 2. 6 3 8 0. 37 + 13. 5 + 2. 638 = is changed to: Or better 0 1 3 + 2 1 6 . 3. 5. 6. 5 7 0 3 0 0 0 8 8
Try this one next… Example add: 0. 2 3 6 2. 4 + 2. 8 7 0. 236 + 2. 4 + 2. 87 = is changed to: Or better
Try this one next… Example add: 0. 2 3 6 2. 4 + 2. 8 7 0. 236 + 2. 4 + 2. 87 = is changed to: Or better 0 2 + 2 5 . 2. 4. 8. 5 3 0 7 0 6 0 0 6
Subtracting decimals is much like adding decimals, but you subtract AFTER you line up the decimals in one column. Example subtract: 1 2. 5 1 2 - 8. 7 14. 512 – 8. 7 = is changed to: Or better 1 2. 5 1 2 - 8. 7 0 0 3. 8 1 2
Try this one next… Example subtract: - 9. 0 3. 6 0 4 9. 0 – 3. 604 = is changed to: Or better
Try this one next… Example subtract: - 9. 0 3. 6 0 4 9. 0 – 3. 604 = is changed to: 8 Or better - 9 9 1 9. 0 0 0 3. 6 0 4 5. 3 9 6
Try these two next… 1 2. 5 - 0. 7 Then… 1 7. 2 9 4 - 0. 8
Try these two next… 1 2. 5 - 0. 7 1 1. 8 Round this one to the nearest WHOLE NUMBER Then… 6 1 1 7. 2 9 4 - 0. 8 0 0 1 6. 4 9 4 Round this one to the nearest TENTH
Try these two next… 1 2. 5 - 0. 7 1 1. 8 Round this one to the nearest WHOLE NUMBER 11. 8 rounds to 12 Then… 6 1 1 7. 2 9 4 - 0. 8 0 0 1 6. 4 9 4 Round this one to the nearest TENTH This rounds to 16. 5
Multiplication of Decimals The rules here are, multiply the numbers, then adjust the decimal in the answer. There has to be the same number of decimal places in the answer as the total in the math. Example: 2. 6 x. 45 becomes… 2. 6 x. 45 THERE ARE 1 AND 2 DECIMAL PLACES = 3 TOTAL DECIMAL PLACES IN THE MATH. 26 x 45 130 SO WE CHANGE 1170 TO + 1040 1170 → 1. 170
Try this one… Example: 5. 3 X 0. 5 becomes…
Try this one… Example: 5. 3 X 0. 5 becomes… 5. 3 x 0. 5 THERE ARE 1 AND 1 DECIMAL PLACES = 2 TOTAL DECIMAL PLACES IN THE MATH. 5. 3 x 0. 5 265 → SO WE CHANGE 265 TO 2. 65
Division of Decimals The rules here are, figure out where the decimal belongs in the answer before you divide the numbers. Put the decimal point in the QUOTIENT right above the one inside the division “box” Example: Divide 14. 4 by 6 will become… 6 14. 4
Division of Decimals The rules here are, figure out where the decimal belongs in the answer before you divide the numbers. Put the decimal point in the QUOTIENT right above the one inside the division “box” 2. 4 Example: Divide 14. 4 by 6 will become… 6 14. 4 -12 24 - 24 0
Try this one… Example: Divide 20. 45 by 5 will become… 5 20. 45
Try this one… Example: Divide 20. 45 by 5 will become… 4. 09 5 20. 45 - 20 4 45 - 45 0
There’s one trick in Division of decimals… If the divisor is a decimal, you must move the decimal points before you start in BOTH divisor and dividend before you start. Example: divide 4. 9 by 0. 35 becomes… 14. 0. 35 4. 9 which must become 35 490.
There’s one trick in Division of decimals… If the divisor is a decimal, you must move the decimal points before you start in BOTH divisor and dividend before you start. Example: divide 4. 9 by 0. 35 becomes… 14. 0. 35 4. 9 which must become 35 490. - 35 140 - 140 0
Try these four now… rewrite them as necessary ADD 2. 8 and 9. 46 SUBTRACT 10 minus 7. 89 MULTIPLY 13. 5 times 0. 25 DIVIDE 2. 76 by 0. 6
ADD 2. 8 and 9. 46 Becomes…
ADD 2. 8 and 9. 46 Becomes… 2. 80 + 9. 46 12. 26
SUBTRACT 10 minus 7. 89 Becomes…
SUBTRACT 10 minus 7. 89 Becomes… 1 0. 0 0 - 7. 8 9 2. 1 1
MULTIPLY 13. 5 times 0. 25 Becomes… You do not have to line up the decimals in multiplication, just count the places, and fix your answer.
MULTIPLY 13. 5 times 0. 25 Becomes… 13. 5 X. 25 1 0 x 2 5 5 2 6 2 5 The answer must get 3 decimal places… The right answer is 2. 625
DIVIDE 2. 76 by 0. 6 Becomes… 0. 6 2. 76 Which changes to…
DIVIDE 2. 76 by 0. 6 Becomes… 0. 6 2. 76 Which changes to… 4. 6 6 27. 6 - 24 36 - 36 0
Homework problems Some rounding from last week, then some decimal addition, subtraction, multiplication and division. J
- Slides: 29