10,579
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Line 55:
Line 55: + + + + + + + + + +
→Addition
To add, simply move in more beads to represent the number you are adding. There are two rules to follow: (1) whenever you have a total of 5 units or more on the bottom of a column, cancel out the 5 by sliding the beads back down and add a five to to the top; and (2) whenever you have a total of 10 units or more in a column, cancel out the 10 and add one unit to the column immediately to the left. (With the nepohualtzintzin, you work with 20 rather than 10.)
To add, simply move in more beads to represent the number you are adding. There are two rules to follow: (1) whenever you have a total of 5 units or more on the bottom of a column, cancel out the 5 by sliding the beads back down and add a five to to the top; and (2) whenever you have a total of 10 units or more in a column, cancel out the 10 and add one unit to the column immediately to the left. (With the nepohualtzintzin, you work with 20 rather than 10.)
<gallery>
File:Abacus-plus-4.png|4
File:Abacus-plus-3.png|+3 (5–2=3)
File:Abacus-plus-5.png|+5
File:Abacus-12.png|carry 5s to next column
File:Abacus-plus-19.png|+19 (20-1=19)
File:Abacus-plus-24.png|+24
File:Abacus-55,png|4+3+5+19+24=55
</gallery>
=== Subtraction ===
=== Subtraction ===