Explain Addition and Subtraction Strategies - 2nd Grade Math
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What is $52 - 8$ by breaking $8$ into $2 + 6$?
What is $52 - 8$ by breaking $8$ into $2 + 6$?
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$44$. First subtract 2 to get 50, then subtract remaining 6: $50 - 6 = 44$.
$44$. First subtract 2 to get 50, then subtract remaining 6: $50 - 6 = 44$.
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What is $50 - 26$ using the idea $50 - 26 = 40 - 16$?
What is $50 - 26$ using the idea $50 - 26 = 40 - 16$?
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$24$. Regroup: borrow 1 ten from 50, making it $40 + 10 - 26 = 24$.
$24$. Regroup: borrow 1 ten from 50, making it $40 + 10 - 26 = 24$.
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What is $61 - 27$ using the idea $61 - 27 = 61 - 20 - 7$?
What is $61 - 27$ using the idea $61 - 27 = 61 - 20 - 7$?
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$34$. First subtract 20 to get 41, then subtract 7: $41 - 7 = 34$.
$34$. First subtract 20 to get 41, then subtract 7: $41 - 7 = 34$.
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What is $48 + 19$ using compensation: $48 + 19 = 48 + 20 - 1$?
What is $48 + 19$ using compensation: $48 + 19 = 48 + 20 - 1$?
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$67$. Round 19 up to 20, add to get 68, then subtract 1: $68 - 1 = 67$.
$67$. Round 19 up to 20, add to get 68, then subtract 1: $68 - 1 = 67$.
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What is $62 - 19$ using compensation: $62 - 19 = 62 - 20 + 1$?
What is $62 - 19$ using compensation: $62 - 19 = 62 - 20 + 1$?
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$43$. Round 19 up to 20, subtract to get 42, then add back 1: $42 + 1 = 43$.
$43$. Round 19 up to 20, subtract to get 42, then add back 1: $42 + 1 = 43$.
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What is $73 - 30$ using place value (subtract tens)?
What is $73 - 30$ using place value (subtract tens)?
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$43$. Subtract tens from tens: $70 - 30 = 40$, keep the 3 ones.
$43$. Subtract tens from tens: $70 - 30 = 40$, keep the 3 ones.
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What is $64 - 20$ using place value (subtract tens)?
What is $64 - 20$ using place value (subtract tens)?
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$44$. Subtract tens from tens: $60 - 20 = 40$, keep the 4 ones.
$44$. Subtract tens from tens: $60 - 20 = 40$, keep the 4 ones.
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What is $39 + 24$ using compensation: $39 + 24 = 40 + 23$?
What is $39 + 24$ using compensation: $39 + 24 = 40 + 23$?
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$63$. Round 39 up to 40, then subtract 1 from 24 to keep the sum equal.
$63$. Round 39 up to 40, then subtract 1 from 24 to keep the sum equal.
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What is $27 + 35$ by adding tens then ones?
What is $27 + 35$ by adding tens then ones?
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$62$. Add tens ($20 + 30 = 50$), then add ones ($7 + 5 = 12$), so $50 + 12 = 62$.
$62$. Add tens ($20 + 30 = 50$), then add ones ($7 + 5 = 12$), so $50 + 12 = 62$.
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What is $58 + 7$ by adding ones first?
What is $58 + 7$ by adding ones first?
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$65$. Add ones: $8 + 7 = 15$, which is 1 ten and 5 ones, so $50 + 15 = 65$.
$65$. Add ones: $8 + 7 = 15$, which is 1 ten and 5 ones, so $50 + 15 = 65$.
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What is $46 + 30$ using place value tens and ones?
What is $46 + 30$ using place value tens and ones?
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$76$. Add tens to tens: $40 + 30 = 70$, keep the 6 ones.
$76$. Add tens to tens: $40 + 30 = 70$, keep the 6 ones.
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Identify the property used to make a ten: $8 + 6 = 8 + 2 + 4$.
Identify the property used to make a ten: $8 + 6 = 8 + 2 + 4$.
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Associative property of addition. Breaks 6 into 2+4 to make 10 with 8, then adds remaining 4.
Associative property of addition. Breaks 6 into 2+4 to make 10 with 8, then adds remaining 4.
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Which property is shown by $8 + (2 + 5) = (8 + 2) + 5$?
Which property is shown by $8 + (2 + 5) = (8 + 2) + 5$?
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Associative property of addition. Grouping doesn't change the sum when adding three numbers.
Associative property of addition. Grouping doesn't change the sum when adding three numbers.
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What property is shown by $7 + 0 = 7$?
What property is shown by $7 + 0 = 7$?
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Additive identity property. Adding zero to any number gives the same number.
Additive identity property. Adding zero to any number gives the same number.
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What property is shown by $(10 + 6) + 4 = 10 + (6 + 4)$?
What property is shown by $(10 + 6) + 4 = 10 + (6 + 4)$?
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Associative property of addition. Grouping doesn't change the sum when adding three numbers.
Associative property of addition. Grouping doesn't change the sum when adding three numbers.
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