1. What is an abacus? 
2. How does an abacus work for subtraction? 
3. What are complementary numbers respect to 10? 
4. How do you represent numbers in the hundred's column on an abacus? 
5. Can an abacus be used for other mathematical operations? 
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 
Abacus Lesson 31 // SUBTRACT COMPOUND Complementary Numbers Respect to 10 ONE'S Column Video  07:36 min 
Abacus Lesson 32 // SUBTRACT COMPOUND Complementary Numbers Respect to 10 TEN'S Column Video  06:29 min 

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