Add Near Doubles from a Double You Know
If you know a double, the neighbor is one more or one less than that double.
A double is the same number added to itself: 6 + 6, 7 + 7, 8 + 8. A near double is one step away from that. If you already know the double, you do not start the problem over. You add 1 or take 1 away.
6 + 7 sits next to 6 + 6. 7 is 6 plus 1, so the problem is the double and one extra. 6 + 6 = 12, and 12 + 1 = 13.
6 + 6 + 1
Keep the double together.
12 + 1 = 13
Add the extra 1.
- Find the double hiding beside the problem.
- Add that double.
- If the neighbor is one more, add 1.
- If the neighbor is one less, subtract 1.
8 + 7 is next to 8 + 8. 8 + 8 = 16, and 7 is one less than 8, so take 1 away: 16 − 1 = 15. 5 + 6 is next to 5 + 5. 5 + 5 = 10, then 10 + 1 = 11.
Watch out
- Doubling the larger number and still adding 1. 8 + 7 is 16 − 1, not 16 + 1.
- Forgetting whether the neighbor is one more or one less.
- Starting from a double you do not know yet. Use the double you can say.
What is 8 + 7?
8 + 8 = 16, and 7 is one less, so 16 − 1 = 15.
What is 9 + 8?
8 + 8 = 16, and 9 is one more, so 16 + 1 = 17. From the other side, 9 + 9 = 18, then 18 − 1 = 17.
Math practice for Near Doubles
Add within 20
Practice this