R.4 Subtract zeros and doubles - up to 20
What does it mean to subtract?
Subtraction means taking away from a number to find out how many are left.
- 5 − 2 = 3
- 10 − 4 = 6
When you subtract, the answer is usually smaller than the number you started with.
Subtracting zero
When you subtract zero from a number, the number stays the same. Zero means nothing is taken away.
- 7 − 0 = 7
- 15 − 0 = 15
- 20 − 0 = 20
If you see a subtraction problem with zero, you can quickly write the first number as the answer.
What are doubles?
Doubles are numbers made by adding the same number to itself, such as 4 + 4 or 6 + 6.
- 3 + 3 = 6
- 5 + 5 = 10
- 8 + 8 = 16
Knowing doubles helps you subtract faster.
Subtracting doubles
When you subtract a number from its double, the answer is the number itself.
- 6 − 3 = 3
- 10 − 5 = 5
- 14 − 7 = 7
Think: “Two of the same number minus one leaves one.”
Subtracting doubles up to 20
You can use doubles to subtract numbers up to 20 by recognizing equal groups.
- 12 − 6 = 6
- 16 − 8 = 8
- 18 − 9 = 9
If the first number is twice as big as the second number, the answer is the second number.
Common Core alignment: CCSS.MATH.CONTENT.1.OA.C.6 – Add and subtract within 20.
Notes for teachers
This free lesson is aligned with CCSS.MATH.CONTENT.1.OA.C.6. Use it for whole-class instruction, small groups, or independent practice.
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