Abacus Lesson 9: Addition, Complements of 5, 1's column

Complements of a number are 2 numbers which together adds up to the first number.
Complements of a 5 are 2 numbers which together adds up to 5.
Complements of 5 are 4 & 1, 3 & 2, 2 & 3, 1 & 4
We use complements when we run out of earthly beads

For additions, we take away complements when we are doing additions.

Example, 1 + 4
1 bead is already touching the beam
take away 1, then slide 5 down to touch the beam

Example, 2 + 3
2 beads already touching the beam
take away 2, then slide 5 down

Example, 4 + 2
Complement of 2 is 3
Take away 3, then add 5

Example, 4 + 3
Complement of 3 is 2
Take away 2, then add 5

Example, 4 + 4
Complement of 4 is 1
Take away 1, add 5

Example, 2 + 4
Complement of 4 is 1
Take away 1, add 1

Now do the worksheets

Video: Abacus Lesson 9: Addition, Complements of 5, 1's column



Acknowledgement: Credit to John of HEV Project. This post is a summary of HEV Abacus Lessons