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Mathematics Chapter 1: Addition & Subtraction with regrouping Grassy Lake Elementary School Third Grade Created by: Mrs. Tamara Russell
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Goals To identify and write related addition and subtraction facts. To solve number sentences for missing addends. To add 2-digit numbers without regrouping. To subtract 2-digit numbers without regrouping. To use the problem solving skill choose the operation.
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Materials Scrap paper or white boards Pencils or expo markers Erasers or paper towels for the boards
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Today’s Lesson By the end of today’s lesson, you will be able to add and subtract two digit numbers using regrouping. 56 +15 71 62 - 15 47 151
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Lesson Did you know that every number has a home, just like you? We call those numbers homes their place value. In order to add or subtract two digit numbers we need to review place value! Let’s go!
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Let’s do some problems! You will need a white board, a marker and an eraser. Together we will do six problems – three addition and three subtraction. When we are all done, we should know how to add and subtract by regrouping! Let’s do it!
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Two digit addition Always remember to line up your numbers properly. Start at the right. (6 + 5) Put the sum of 6 + 5 in its house. (11) Oops! Too many! Carry a number! Now, add the numbers in the tens’ column. (5 + 1 + 1) Put the sum of 5 + 1 + 1 in the tens’ column. (7) 5 6 + 1 5 TensOnes 17 1
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Again? Always remember to line up your numbers properly. Start at the right. (4 + 6) Put the sum of 4 + 6 in its house. (10) Oops! Too many! Carry a number! Now, add the numbers in the tens’ column. (2 + 3 + 1) Put the sum of 2 + 3 + 1 in the tens’ column. (6) 6 4 + 3 2 TensOnes 06 1
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Last time? Always remember to line up your numbers properly. Start at the right. (2 + 9) Put the sum of 2 + 9 in its house. (11) Oops! Too many! Carry a number! Now, add the numbers in the tens’ column. (3 + 1 + 1) Put the sum of 3 + 1 + 1 in the tens’ column. (5) 9 2 + 1 3 TensOnes 15 1
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Let’s subtract! Always remember to line up your numbers properly. Start at the right. (3 - 4) Oops! You can’t subtract 4 from 3! Time to borrow! Borrow ten from next door and make 13. And subtract a ten to make 6. Now, subtract. (13 – 4) Put your answer in the ones place. Last, subtract 6 – 3. Put your answer in the tens place! 4 3 - 3 7 TensOnes 93 13 6
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Again? Always remember to line up your numbers properly. Start at the right. (2 - 4) Oops! You can’t subtract 4 from 2! Time to borrow! Borrow ten from next door and make 12. And subtract a ten to make 6. Now, subtract. (12 – 4) Put your answer in the ones place. Last, subtract 3 – 2. Put your answer in the tens place! 4 2 - 2 4 TensOnes 81 123
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Last time! Always remember to line up your numbers properly. Start at the right. (5 - 9) Oops! You can’t subtract 5 from 9! Time to borrow! Borrow ten from next door and make 15. And subtract a ten to make 7. Now, subtract. (15 – 9) Put your answer in the ones place. Last, subtract 7 – 7. The answer is zero and does not change the amount in the number, so you don’t have to put it there! 9 5 - 7 8 TensOnes 6 157
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Independent work Complete these practice problems on your white board. Raise your hand when you are done so that I can check your work! You have ten minutes to work and then I’ll show you the answers. 24 64 + 16- 58 23 78 + 48- 59 40 1 71 1 6 514 19 618
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Fantastic! How did I get such smart cookies? Tomorrow’s Lesson: Working on addition and subtraction story problems
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