Fluent adding and subtracting within 20

Fluently add and subtract within 20 using mental strategies; know from memory all sums of two one-digit numbers

Usually learned at ages 7–8

Builds on: Addition and subtraction within 20, Fluent adding and subtracting within 10

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On the map from: Marble Skill Taxonomy (v1), © Generative Spark, Inc. (withmarble.com), text CC BY-SA 4.0, database ODbL 1.0: https://github.com/withmarbleapp/os-taxonomy