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Addition and Subtraction 29

Addition and Subtraction Algorithms. 2 ones plus 9 ones equal 11 ones. 11 is 1 ten and 1 one. Record the 1 one in the ones column between the equals sign. Because we have more tens, we record the 1 ten in the tens column above the equals sign. 8 tens plus 8 tens plus 1 ten equals 17 tens.

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Addition and Subtraction 29

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  1. Addition and Subtraction Algorithms 2 ones plus 9 ones equal 11 ones. 11 is 1 ten and 1 one. Record the 1 one in the ones column between the equals sign. Because we have more tens, we record the 1 ten in the tens column above the equals sign. 8 tens plus 8 tens plus 1 ten equals 17 tens. 17 tens is 1 hundred and 7 tens. Record the 7 tens in the tens column between the equals sign. Because we have more hundreds, we record the 1 hundred in the hundreds column above the equals sign. 1 1 6 8 2 + 5 8 9 1 7 Addition and Subtraction 29

  2. Addition and Subtraction Algorithms 2 ones plus 9 ones equal 11 ones. 11 is 1 ten and 1 one. Record the 1 one in the ones column between the equals sign. Because we have more tens, we record the 1 ten in the tens column above the equals sign. 8 tens plus 8 tens plus 1 ten equals 17 tens. 17 tens is 1 hundred and 7 tens. Record the 7 tens in the tens column between the equals sign. Because we have more hundreds, we record the 1 hundred in the hundreds column above the equals sign. 6 hundreds plus 5 hundreds plus 1 hundred is 12 hundreds. 12 hundred is 1 thousand and 2 hundreds. Because we have no more thousands, we can record the 1 thousand and 2 hundreds in the thousands and hundreds columns between the equals sign. 16 18 2 + 5 8 9 7 1 1 2 Addition and Subtraction 29

  3. Addition and Subtraction Algorithms 682 + 589 = + 400 + 100 + 20 + 60 + 8 + 1 682 1082 1182 1202 1262 1270 1271 682 + 589 = 682 + 600 = 1282 1282 - 11 = 1271 682 + 589 = 1271 Addition and Subtraction 29

  4. Addition and Subtraction Algorithms I don’t have enough ones to subtract 8 ones from 7 ones. So I can add ten to both numbers without changing the difference between them. I’ll add 10 ones as 10 ones to the top number. And I’ll add 10 ones as 1 ten to the bottom number. 17 ones minus 8 ones equals 9 ones. We’ll record the 9 ones in the ones column between the equals sign. 1 1 2 7 - 5 8 1 9 Addition and Subtraction 29

  5. Addition and Subtraction Algorithms I don’t have enough ones to subtract 8 ones from 7 ones. So I can add ten to both numbers without changing the difference between them. I’ll add 10 ones as 10 ones to the top number. And I’ll add 10 ones as 1 ten to the bottom number. 17 ones minus 8 ones equals 9 ones. We’ll record the 9 ones in the ones column between the equals sign. I don’t have enough tens to subtract 6 tens from 2 tens. So I can add 10 tens to both numbers without changing the difference between them. I’ll add 10 tens as 10 tens to the top number. And I’ll add 10 tens as 1 hundred to the bottom number. 12 tens minus 5 tens is 7 tens. We’ll record the 7 tens in the tens column between the equals sign. 1 1 1 2 7 - 5 8 1 1 7 9 Addition and Subtraction 29

  6. Addition and Subtraction Algorithms I don’t have enough ones to subtract 8 ones from 7 ones. So I can add ten to both numbers without changing the difference between them. I’ll add 10 ones as 10 ones to the top number. And I’ll add 10 ones as 1 ten to the bottom number. 17 ones minus 8 ones equals 9 ones. We’ll record the 9 ones in the ones column between the equals sign. I don’t have enough tens to subtract 6 tens from 2 tens. So I can add 10 tens to both numbers without changing the difference between them. I’ll add 10 tens as 10 tens to the top number. And I’ll add 10 tens as 1 hundred to the bottom number. 12 tens minus 6 tens is 6 tens. We’ll record the 6 tens in the tens column between the equals sign. 1 hundred plus 1 hundred equals 2 hundred. We’ll record the 2 hundred in the hundreds column between the equals sign. 1 1 1 2 7 - 5 8 1 1 6 9 Addition and Subtraction 29

  7. Addition and Subtraction Algorithms I don’t have enough ones to subtract 8 ones from 7 ones. So I can change 1 ten into 10 ones. Now I have 1 ten and 17 ones. 17 ones minus 8 ones equals 9 ones. We’ll record the 9 ones in the ones column between the equals sign. 1 1 1 2 7 - 5 8 9 Addition and Subtraction 29

  8. Addition and Subtraction Algorithms I don’t have enough ones to subtract 8 ones from 7 ones. So I can change 1 ten into 10 ones. Now I have 1 ten and 17 ones. 17 ones minus 8 ones equals 9 ones. We’ll record the 9 ones in the ones column between the equals sign. I don’t have enough tens to subtract 5 tens from 1 ten. So I can change 1 hundred into 10 tens. Now I have zero hundreds and 11 tens. 11 tens minus 5 tens equals 6 tens. 0 1 1 1 1 2 7 - 5 8 6 9 Addition and Subtraction 29

  9. Addition and Subtraction Algorithms • 127 - 58 = - 1 - 7 - 30 - 20 69 70 77 107 127 127 - 58 = 127 - 60 =67 67 + 2 = 69 127 - 58 = 69 Addition and Subtraction 29

  10. Addition and Subtraction Algorithms • What numbers did you select? • How did you add / subtract your numbers? • Was your strategy or an algorithm more efficient? Why? • The numbers I selected are ... • I added / subtracted using my strategy / an algorithm by ... • The most efficient way was ... because ... Addition and Subtraction 29

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