Abacus Lesson 33: Subtraction, Compound Complementary Numbers, 100's column

872 - 216
100's column, take away 2
10's column, take away 1
1's column, Compound complement of 6 is 1
Take away 1, add 5, take away 1 in 10's column
Answer is 656


683 - 126
100's column, take away 1
10's column, take away 2
1's column, compound complement of 6 is 1
Take away 1, add 5, take away 10
Answer is 557

791 - 126
100's column, take away 1
10's column, take away 2
1's column, compound complement of 6 is 1
Take away 1, add 5, take away 10
Answer is 665

231 - 180
100's column, take away 1
10's column, compound complement of 8 is 3
Take away 3, add 5, take away 1 next column
1's column, take away nothing
Answer is 51

791 - 508
100's column, take away 5
10's column, do nothing
1's column, compound complement is 8
Take away 3, add 5, take away 1 in next column
Answer is 406

Do Worksheet 33 now, make own questions, practice, practice, practice till action is mechanical

Video: Abacus Lesson 33: Subtraction, Compound Complementary Numbers, 100's column

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