12 + 9
Complement of 9 is 1
Take away 1, add 10
Answer is 21
22 + 18
Do from left to right, so do the 10s column first, then the 1 column
Add 1 in the 10 column
Compliment of 8 is 2
Take away 2 in the 1 column, add 10 (add 1 in the 10 column)
Answer is 40
16 + 19
Do from left to right, so do the 10s column first, then the 1 column
Add 1 in the 10 column
Compliment of 9 is 1
Take away 1 in the 1 column, add 10
Answer is 35
99 + 10
Do from left to right, so do the 10s column first, then the 1 column
Add 1 in the 10s column
Compliment of 1 is 9
Take away 9 in the 10s column, add 1 in the 100s column)
109
55 + 55
Do from left to right, so do the 10s column first, then the 1s column
In the 10s column, complement of 5 is 5
Take away 5 in the 10s column, add 1 in the 100s columnf
In the 1s column, complement of 5 is 5
Take away 5 in the 1s column, add 1 in the 10s column
Answer is 110
8 + 37
In the 10s column, add 3
In the 1s column, complement of 7 is 3
Take away 3 in the 1s column, add 1 in the 10s column
Answer is 45
64 + 26
In the 10s column, add 2
In the 1s column, complement of 6 is 4
In the 1s column, take away 4, add 10
Answer is 90
Video: Abacus Lesson 23: Addition, Complementary Numbers Respect to 10's Column
Source: HEV Project: Abacus Lesson 23: Addition - Complementary Numbers Respect to 10's Column
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