1. What is an abacus? 
2. What is subtraction with complementary numbers respect to 10? 
3. How do you perform subtraction using the abacus in the one's column? 
4. Why is it important to learn subtraction on an abacus? 
5. What are some advantages of using an abacus for subtraction? 
Abacus Lesson 26 // SubtractionComplementary Numbers Respect to 10 TEN'S Column Video  07:45 min 
Abacus Lesson 27 // SubtractionComplementary Numbers Respect to 10 HUNDRED'S Column Video  05:08 min 
Abacus Lesson 28 // ADD COMPOUND Complementary Numbers Respect to 10 ONE'S Column Video  08:50 min 
Abacus Lesson 29 // ADD COMPOUND Complementary Numbers Respect to 10 TEN'S Column Video  13:00 min 
Abacus Lesson 30 // ADD COMPOUND Complementary Numbers Respect to 10 HUNDRED'S Column Video  09:08 min 

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