Activities/Abacus: Difference between revisions
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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 === | ||