This post is about Complementary numbers with respect to 10
Lessons 20 teaches that the complementary numbers w.r.t. 10 are:
9 and 1, 1 and 9
8 and 2, 2 and 8
7 and 3, 3 and 7
6 and 4, 4 and 6
5 and 5, 5 and 5
Requires learner to memorize the complements of 10
Think of 1 when 9 is involved
Think of 9 when 1 is involved
Think of 8 when 2 is involved
Think of 2 when 8 is involved
Think of 7 when 3 is involved
Think of 3 when 7 is involved
etc, etc
Suggestion is to make flash cards
Video:
Acknowledgement: Credit to John of HEV Project for the abacus lesson videos and worksheet
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