O.2 Add doubles, doubles plus one, and doubles minus one
What are doubles?
Doubles are addition facts where both numbers are the same. You add a number to itself.
- 2 + 2 = 4
- 5 + 5 = 10
- 9 + 9 = 18
Doubles are helpful because they are easy to remember and help you add faster.
Common doubles facts
These are doubles facts using numbers from 0 to 10. All sums are 20 or less.
- 0 + 0 = 0
- 1 + 1 = 2
- 2 + 2 = 4
- 3 + 3 = 6
- 4 + 4 = 8
- 5 + 5 = 10
- 6 + 6 = 12
- 7 + 7 = 14
- 8 + 8 = 16
- 9 + 9 = 18
- 10 + 10 = 20
Knowing these doubles helps you solve harder addition problems.
What is doubles plus one?
Doubles plus one means you start with a double and then add one more.
- 4 + 5 = 9 (double 4 is 8, plus 1 more)
- 6 + 7 = 13 (double 6 is 12, plus 1 more)
- 2 + 3 = 5 (double 2 is 4, plus 1 more)
Look for the smaller number to find the double.
What is doubles minus one?
Doubles minus one means you start with a double and then subtract one.
- 5 + 4 = 9 (double 5 is 10, minus 1)
- 7 + 6 = 13 (double 7 is 14, minus 1)
- 3 + 2 = 5 (double 3 is 6, minus 1)
If the numbers are one apart, you can use doubles minus one.
Using doubles strategies to add
You can use doubles, doubles plus one, or doubles minus one to help you add quickly and correctly.
- 8 + 8 = 16 (doubles)
- 8 + 9 = 17 (doubles plus one)
- 9 + 8 = 17 (doubles minus one)
Ask yourself: Are the numbers the same or close to the same?
Common Core alignment: CCSS.MATH.CONTENT.1.OA.C.6 – Add and subtract within 20, demonstrating fluency for addition.
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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