10,579
edits
Changes
→Subtraction
File:Abacus-minus-6.png|–6=14
File:Abacus-minus-6.png|–6=14
File:Abacus-minus-10.png|–10=4
File:Abacus-minus-10.png|–10=4
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=== Multiplication ===
There are several strategies for doing multiplication on an abacus. In the method used in the example below, the multiplier is stored on the far left of the abacus and the multiplicand is offset to the left by the number of digits in the multiplier. The red ''indicator'' is used to help keep track of where we are in the process.
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File:Abacus-486x24.png|486×24=? Begin by placing 24 in the left-most columns and 486 offset from the far right by two columns (since 24 has two digits). Set the indicator to the right of the multiplicand.
File:Abacus-4x6.png|Multiply the least-significant digits (LSD) of the multiplier (4) and multiplicand (6) and place the results (4×6=24) in the far right columns.
File:Abacus-2x6.png|Multiply the next digit in the multiplier (2, which corresponds to 2×10=20) and the LSD of the multiplicand (6) and add the results (2×6=12) on the right (advancing one column to the left to correspond to the power of the digit in the multiplier).
File:Abacus-100s.png|Move the indicator over one column to the left.
File:Abacus-4x8.png|Repeat for the next digit in the multiplicand (8): 4×8=32
File:Abacus-2x8.png|2×8=16
File:Abacus-1000s.png|Move the indicator over one column to the left.
File:Abacus-4x4.png|Repeat for the next digit in the multiplicand (4): 4×4=16
File:Abacus-2x4.png|2×4=8
File:Abacus-11664.png|Clear the multiplier from the left and view the result: 486×24=11664
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