"Make ten" strategy for addition (1st grade math)
A lesson about the concept in addition that I've termed "going over to the next ten". We have either two single-digit numbers or one two-digit and one single-digit number to add. Essentially, you first make ten, and then check what you have "left over".
This strategy promotes number sense (very important for elementary grades) and conceptual understanding.
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See also
Addition facts — online practice (includes an option for missing number additions)
Mental math trick with nine and eight
Math Mammoth Grade 1 curriculum