Abacus Lesson 31: Subtraction, Compound complementary Numbers, 10's column

13 - 6 (13 minus 6)
Addition involving subtraction of complements of 6
Complement of 6 is 4, complement of 4 w.r.t. 5 is 1
Add 1, take away 5, add 10
Subtraction, do opposite of above,
Take away 1, add 5, take away 10
Answer is 7
14 - 9
Complement of 9 is 1, complement of 1 w.r.t. 5 is 4
Take away 4, add 5, take away 1 in 10's column (carry)
Answer is 5

12 - 6
Complement of 6 is 4, compound complement of 4 is 1
Take away 1, add 5, take away 10
Answer is 6

13 - 7
Complement of 7 is 3, compound complement of 3 is 2
Take away 2, add 5, take away 10
Answer is 6

11 - 6
Complement of 6 is 4, compound complement of 4 is 1
Take away 1, add 5, take away 10
Answer is 5

14 - 8
Complement of 8 is 2, compound complement of 2 is 3
Take away 3, add 5, take away 10
Answer is 6

13 - 8
Compound complement of 8 is 3
Take away 3, add 5, take away 10
Answer is 5

Make flash cards (To remember)
Compound complement of 6 is 1
Compound complement of 7 is 2
Compound complement of 8 is 3
Compound complement of 9 is 4

Practice often so certain set of numbers triggers certain mechanical actions and get used to them

Do Worksheet 31 now:

Video: Subtraction, Compound complementary Numbers, 10's column

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