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W.1 Addition and subtraction equations up to 20

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Understanding Equations with Addition and Subtraction

An equation is like a balance. Both sides must be equal. We can use addition and subtraction together in the same equation to make both sides the same.

Examples:
  • 8 − 3 = 4 + 1 means both sides equal 5.
  • 6 + 7 = 10 + 3 shows that both sides equal 13.
  • 9 − 2 = 3 + 4 means both sides equal 7.
Helpful Hint

Always check both sides of the equation. If they match, the equation is true.

Finding the Missing Number

Sometimes an equation has a missing number. We can solve for it by making both sides equal.

Examples:
  • 8 − [ ] = 3 + 2. Since 3 + 2 = 5, the missing number is 3 because 8 − 3 = 5.
  • 10 + [ ] = 14 − 2. The right side is 12, so the missing number is 2 because 10 + 2 = 12.
  • [ ] + 6 = 15 − 4. The right side is 11, so the missing number is 5 because 5 + 6 = 11.
Helpful Hint

Use what you know about number facts to find the missing part. You can check by replacing the number and seeing if both sides match.

Using a Balance Model

Think of equations like a balance scale. Both sides must weigh the same. If one side is heavier or lighter, the equation is not true.

Examples:
  • 7 + 5 is the same as 10 + 2. Both equal 12.
  • 16 − 4 is the same as 8 + 4. Both equal 12.
Helpful Hint

If one side of the equation is bigger, you can add or subtract to make them equal. Equations must always stay balanced.

Checking Your Work

After solving an equation, check your answer. Both sides should equal the same number. If they do not, try again.

Examples:
  • 9 − 4 = 2 + 3. Left side: 5. Right side: 5. The equation is true.
  • 6 + 8 = 20 − 4. Left side: 14. Right side: 16. Not equal, so it is false.
Helpful Hint

Always solve both sides separately before comparing them. True equations have the same value on both sides.

Math in Everyday Life

We use equations in real life when we compare, share, or figure out if two groups are equal.

Real-Life Examples:
  • You have 12 apples. You give away 4. Your friend has 5 + 3 apples. Both sides equal 8, so the groups are equal.
  • A class has 10 boys and 6 girls. Another class has 12 + 4 students. Both sides equal 16, so the classes are the same size.
Try This

Make your own true or false equations when comparing toys, snacks, or groups of people. See if both sides are equal.

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