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S.1 Complete the subtraction sentences - up to 20

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Understanding Subtraction up to 20

Subtraction means taking away or finding the difference between two numbers. In first grade, we practice subtraction problems where the total and the answer are 20 or less.

Examples:
  • 15 − 6 = 9 means fifteen take away six leaves nine.
  • 18 − 7 = 11 shows eighteen minus seven equals eleven.
  • 12 − 5 = 7 means twelve take away five leaves seven.
Helpful Hint

Subtraction is the opposite of addition. If you know that 7 + 5 = 12, then you also know 12 − 5 = 7 and 12 − 7 = 5.

Taking Away Objects

We can use objects or drawings to see subtraction as taking away from a group.

Examples:
  • You have 10 apples. You eat 3. Now there are 10 − 3 = 7 apples left.
  • Draw 12 stars. Cross out 6. Count the ones left: 12 − 6 = 6.
Helpful Hint

Try using coins, toys, or blocks. Start with a number and take some away to see what is left.

Finding the Missing Number

Sometimes subtraction problems have a missing part. We use what we know about addition and subtraction to solve them.

Examples:
  • ? − 7 = 9. Since 9 + 7 = 16, the missing number is 16.
  • 14 − ? = 6. Think: “What plus 6 equals 14?” The answer is 8.
  • 20 − ? = 12. The missing number is 8.
Helpful Hint

Remember subtraction facts by thinking about addition pairs. If 8 + 6 = 14, then 14 − 8 = 6 and 14 − 6 = 8.

Subtracting on a Number Line

A number line helps us subtract by starting at one number and hopping backward until we reach the answer.

Examples:
  • Start at 16 on the number line. Move 5 steps back. You land on 11. So, 16 − 5 = 11.
  • Start at 13. Move 7 steps back. You land on 6. So, 13 − 7 = 6.
Helpful Hint

Always move to the left when subtracting. The farther you go, the smaller the number becomes.

Subtraction in Everyday Life

We use subtraction every day when we take things away or find how many are left in real situations.

Real-Life Examples:
  • You had 12 toy cars. You gave 4 to your friend. Now you have 12 − 4 = 8 cars left.
  • There were 15 birds on a fence. 7 flew away. Now there are 15 − 7 = 8 birds left.
  • You had 18 grapes. You ate 10. That leaves 18 − 10 = 8 grapes.
Try This

Look around your home or classroom. Start with a group of objects, take some away, and see how many are left.

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