Abacus Lesson 29: Addition, Compound Complements of 10, 10'ss column

15 + 26
Do left to right. Add 2 in 10's column
Complement of 6 is 4, complement of 4 w.r.t. 5 is 1
Add 1, take away 5, add 10
Answer is 41

58 + 16
Left to right, add 1 in 10's column
Complement of 6 is 4, complement of 4 w.r.t. 5 is 1
Add 1, take away 5, add 10
Answer is 74

76 + 17
Left to right, add 1 in 10's column
Complement of 7 is 3, complement of 3 w.r.t. 5 is 2
Add 2, take away 5, add 10
Answer is 93

85 + 28
Complement of 2 is 8, take away 8 in 10's column, add 1 in 100's column
Complement of 8 is 2, complement of 2 w.r.t. 5 is 3
Add 3, take away 5 in 10's column, add 1 in 100's column
Answer is 113

55 + 26
Add 2 in 10's column
Complement of 6 is 4, complement of 4 w.r.t. 5 is 1
Add 1 in 1's column, take away 5, add 1 in 10's column
Answer is 81

27 + 86
Left to right, complement of 8 is 2, take away 2 in 10's column, add 1 in 100's column
Complement of 6 is 4, complement of 4 w.r.t. 5 is 1
Add 1 in 1's column, take away 5, add 1 in 10's column
Answer is 113

38 + 96
Complement of 9 is 1, take away 1 in 10's column, add 1 in 100's column
Complement of 6 is 4, complement of 4 w.r.t. 5 is 1,
Add 1, take away 5, add 1 in 10's column
Answer is 134

77 + 66
Complement of 6 is 4, complement of 4 w.r.t. 5 is 1
Add 1 in 10's column, take away 5, carry 1 next column
Complement of 6 is 4, complement of 4 w.r.t. 5 is 1
Add 1 in 10's column, take away 5, carry 1 next column
Answer is 143

36 + 25
Complement of 2 is 3, take away 5 in 10's column, add 5
Complement of 5 is 5, take away 5, carry 1 over
Answer is 61

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Video: Abacus Lesson 29: Addition, Compound Complements of 10, 10's column

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