Let's solve this step-by-step. The worksheet is about the
Commutative Property of Addition, which states:
>
a + b = b + a
This means that changing the order of the numbers being added does
not change the sum.
We are asked to find the missing number in each equation. Let’s go through each one carefully.
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1. $ 1 + 8 = \boxed{8} + 1 $
✔ Already solved: This shows $1 + 8 = 8 + 1$, which is correct due to commutativity.
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2. $ 2 + \boxed{} = 3 + 2 $
We know $3 + 2 = 5$. So we need $2 + x = 5$ → $x = 3$
✔ Answer:
3
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3. $ 3 + 5 = \boxed{} + 3 $
$3 + 5 = 8$, so we need $x + 3 = 8$ → $x = 5$
✔ Answer:
5
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4. $ 6 + 5 = \boxed{} + 6 $
$6 + 5 = 11$, so $x + 6 = 11$ → $x = 5$
✔ Answer:
5
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5. $ 13 + 14 = 14 + \boxed{} $
By commutative property, $13 + 14 = 14 + 13$
✔ Answer:
13
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6. $ 5 + 2 = \boxed{} + 2 $
$5 + 2 = 7$, so $x + 2 = 7$ → $x = 5$
✔ Answer:
5
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7. $ 12 + 15 = \boxed{} + 12 $
$12 + 15 = 27$, so $x + 12 = 27$ → $x = 15$
✔ Answer:
15
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8. $ 3 + 11 = \boxed{} $
Just compute: $3 + 11 = 14$
✔ Answer:
14
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9. $ 18 + \boxed{} = 9 + 18 $
$9 + 18 = 27$, so $18 + x = 27$ → $x = 9$
✔ Answer:
9
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10. $ \boxed{} + 7 = 7 + 11 $
$7 + 11 = 18$, so $x + 7 = 18$ → $x = 11$
✔ Answer:
11
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11. $ 21 + 10 = \boxed{} + 21 $
$21 + 10 = 31$, so $x + 21 = 31$ → $x = 10$
✔ Answer:
10
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12. $ 5 + 12 = \boxed{} + 5 $
$5 + 12 = 17$, so $x + 5 = 17$ → $x = 12$
✔ Answer:
12
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13. $ 6 + 6 = \boxed{} + 6 $
$6 + 6 = 12$, so $x + 6 = 12$ → $x = 6$
✔ Answer:
6
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14. $ 7 + 2 = 2 + \boxed{} $
$7 + 2 = 9$, so $2 + x = 9$ → $x = 7$
✔ Answer:
7
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✔ Final Answers:
1. 8
2. 3
3. 5
4. 5
5. 13
6. 5
7. 15
8. 14
9. 9
10. 11
11. 10
12. 12
13. 6
14. 7
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📌 Explanation:
All problems use the
commutative property of addition:
> $ a + b = b + a $
So when you see something like $ a + b = \boxed{} + a $, the missing number must be $ b $.
For problems like $ a + b = c $, just add the numbers.
This helps students understand that
order doesn’t matter in addition.
Let me know if you'd like this as a printable answer key!
Parent Tip: Review the logic above to help your child master the concept of properties of addition worksheet 2nd.
