Addition facts to 20 are understood as exact relationships among nonnegative whole-number quantities whose sums range from 0 through 20. Fluency includes recognizing commutative pairs, doubles, make-ten combinations, and decompositions such as , enabling facts to be recalled or derived from known facts rather than counted by ones; this supports efficient mental subtraction and later place-value computation, without extending to larger multi-digit sums.
Addition facts to 20 can be recalled by using facts you already know. One helpful strategy is to make 10.
Example: Find .
So,
You can also remember the commutative pair:
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