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Adding and Subtracting Decimals

Adding and Subtracting Decimals. Combine and Separate Line Up Place Values. Suppose you go to a store and purchase a $21 item and a $8 item. What would you say if the clerk added the items this way? Would you pay $101? Of course not!

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Adding and Subtracting Decimals

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  1. Adding and Subtracting Decimals Combine and Separate Line Up Place Values

  2. Suppose you go to a store and purchase a $21 item and a $8 item. What would you say if the clerk added the items this way? Would you pay $101? Of course not! When we round to estimate we can see the sum should be around 30 not 101. Add and Subtract and Compare 21 +8__ 101 20 +10 30

  3. Place Value 21 + 8 29 • The problem shows the numbers were not lined up correctly. • We need the place values to be lined up. • The 8 should be in the one's place • This answer is reasonable because it is close to our estimated answer 30. • When adding, ones should be added to ones, tens to tens, and hundreds to hundreds. • The same is true for tenths, hundredths, and thousandths.

  4. Understanding Place Value

  5. Place Value Grid Models

  6. Whole number grid models

  7. Decimal Grid Models Money

  8. Decimal Grid Models

  9. Recognize the Decimal

  10. Decimal Problem Solver • Use blank tenths and hundredths grids to model the decimal numbers in each problem. • Cut out and glue each problem and the decimal grids onto construction paper to show how you solved it.

  11. #1 Laura ran 0.4 miles one day and 0.3 miles the second day. How many miles did Laura run altogether? + =

  12. #2 . Juan biked 1.2 miles one day and 1.5 miles the second day. How many miles did Juan bike altogether? + ___________________ .

  13. Try on your own.

  14. Add On your Marker Board • Follow the example: 2.3 + 4 + 5.027 • Even whole numbers have a decimal. • The 4 has a decimal after it.2.3 + 4. + 5.027 • Line up the decimal • Fill in zeroes • Add the place values • Round to the front number or the greatest place to estimate 2 + 4 + 5= 11 2.3 4 + 5.027 2.300 4.000 + 5.027 11.327

  15. Subtract on your Marker Board 12.3 - 5.04 • Put the greater amount as the minuend • It might help to think of the numbers as dollar amounts • Line up the Decimals • Fill in Zeroes • Be sure to regroup carefully • Estimate by rounding to the greatest place to ensure your answer is reasonable. • Watch your teacher work through the problem on the board. • Does the teacher’s estimated answer show a reasonable answer? $12.30 - $ 5.04

  16. On your Marker Board To insure that like place values are added and subtracted, we can line up the decimals. *Work these. *Check with your partner. *Discuss how you estimated by rounding to the greatest place and are confident your answer is correct. #1 82.74 #2 145.12 #3 $ 38.54 - $12.76+ 6.05 - 23.00 #4 67 + 3.98 #5 100 - 34.89Watch the teacher work each problem. How did the answers compare to the estimated answers? How did you estimate? Are your answers close? Did you line the decimals?

  17. Paper AssignmentWrite the problem. Solve carefully. Then show the reasonable estimation. #1 $16.34 + $5.78 #2 $120 – $46.37 #3 765.32 + 12 + 90.8 #4 87 – 64.95 #5 187.543 + 6.246 + 10.8 + 443.67 Be sure to round to the greatest place and estimate to see if your answer is reasonable. Grade/Check: Use a red pen to self check your answers, watch your teacher complete these after you have completed yours on your paper.

  18. Newspaper Assignment • Use the newspaper adds to find items to purchase. Choose items that go together. Example: bread, peanut butter, jelly. These items create a sandwich. • Write the items and the prices, • Add the items. • Now decide the next greatest dollar to pay the cashier. Subtract from the dollar amount you paid the cashier to find your change.

  19. Let’s start together! Name ____________Newspaper Decimals_____________________________________________________________________________________2 items____________3 items __________4 items ______________ cake mix $ 1.09____________________________________________ icing + $ 1.29_____________________________________________total _$ 2.38____________________________________________ _________________________________________________________Pay with $ 5.00 __________________________________________ _______-_$ 2.38 ___________________________________________ change $ 2.62___________________________________________ _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

  20. Review • Locate the decimals • Use the decimals to line up the place values • Use zeroes to organize • Be careful when regrouping • Check your answer • Does your answer make sense? • Practice • Yea! You got it!!

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