Abacus Lesson 22: Addition, Complementary Numbers Respect to 10, 1's Column

This post is a summary to HEV Project Abacus Lesson 22: Addition -Complementary Numbers Respect to 10- ONE'S Column

Using complements of 10 to do addition.
When doing addition, subtract the complement and add 10

3 + 9:
Complement of 9 is 1,
Subtract 1, add 10
Answer is 12

4 + 7
Compliment of 7 is 3
Subtract 3, add 10
Answer is 11

9 + 9
Complement of 9 is 1
Subtract 1, add 10
Answer is 18

4 + 6
Complement os 6 is 4
Subtract 4, add 10
Answer is 10

4 + 9
Complement of 9 is 1
Take away 1, add 10
Answer is 13

9 + 6
Complement of 6 is 4
Take away 4, add 10
Answer is 15

8 + 7
Complement of 7 is 3
Take away 3, add 10
Answer is 15

7 + 9
Complement 9 is 1
Subtract 1, add 10
Answer is 16

Video: Abacus Lesson 22: Addition: Complementary Numbers Respect to 10, 1's Column

Acknowledgement: Credit to John of HEV Project for the abacus lesson videos and worksheet