Addition facts to 20 are the sums of pairs of whole numbers, including zero, whose total is no greater than 20; fluency reflects understanding of relationships such as commutativity, doubles, near-doubles, and decompositions that make ten, rather than treating each fact as unrelated. These facts support efficient mental calculation and subtraction reasoning; this scope does not include multi-digit addition, extended fact families, or generalized algebraic treatment.
Addition facts to 20 are sums you can solve quickly in your head. Use relationships you know, such as making a ten.
Example: Find .
So,
You can also remember that switching the addends does not change the sum: .
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