Abacus Lesson 32: Subtraction, Compound Complementary Numbers, 10's column

73 - 18
10's column, take away 1
1's column, Compound complement of 8 is 3
Take away 3, add 5, take away 1 in 10's column (carry)
Answer is 55


83 - 26
10's column, take away 2
Compound complement of 6 is 1
1's column, Take away 1, add 5, take away 10 (carry 1)
Answer is 57

72 - 16
10's column, take away 1
1's column, Compound complement of 6 is 1
Take away 1, add 5, take away 10 (carry 1)
Answer is 56

23 - 18
10's column, take away 1
1's column, Compound complement of 8 is 3
Take away 3, add 5, take away 10
Answer is 5

91 - 26
10's column, take away 2
1's column, Compound complement of 6 is 1
Take away 1, add 5, take away 10 (carry 1)
Answer is 65

74 - 28
10's column, take away 2
1's column, Compound complement of 8 is 3
Take away 3, add 5, take away 1 in 10's column
10's column, complement of 1 is 4, add 4, take away 5
Answer is 46

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Video: Abacus Lesson 32: Subtraction, Compound Complementary Numbers, 10's column

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