Addition fact · doubles
9 + 9 = 18
Nine plus nine equals eighteen. 9 + 9 is a double: the same number twice. Doubles are worth knowing by heart, because so many other facts lean on them.
See 9 + 9
9 red and 9 yellow. The first frame fills up at 10, and 8 more sit in the next one.
It's a double
- See two equal groups of 9.
- Nine is one less than 10, so 9 + 9 is two less than 10 + 10: 18.
- So 9 + 9 = 18. Say it a few times until it comes without counting.
Its fact family has two facts
9, 9 and 18 go together, so learning one of these helps with all of them. See the family.
Practice 9 + 9 in a game
A fact sticks when a child has to pull it from memory again and again. In this game 9 + 9 keeps coming back between the other facts in its family.
Every round leans on 9 + 9
Free to play · no signup · works on phones, tablets and computers
Quick quiz
9 + 9 FAQ
What is 9 + 9?
9 + 9 = 18. In words: nine plus nine equals eighteen.
Why is 9 + 9 called a double?
Because both numbers are the same. It has a smaller fact family than most: just 9 + 9 = 18 and 18 − 9 = 9.
What grade learns 9 + 9?
This is a first and second grade fact. Common Core has children add within 20 in first grade (1.OA.C.6), and by the end of second grade know all sums of two one-digit numbers from memory (2.OA.B.2).
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An app is on its way
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