Addition on the soroban uses three cases: direct addition, the five-complement, and the ten-complement (carrying). We always start from the ones column.
Conceptos clave
1 1) Direct addition
If enough beads are available, move them directly. Example: 2 + 3 — raise three earth beads to get 5 (which can be swapped for the heaven bead).
2 2) Five-complement
When adding a digit and there aren’t enough earth beads, use the heaven bead (5). Rule: add 5 and subtract the complement to 5. Example 4 + 3: since 3 = 5 − 2, lower the heaven bead (+5) and lower two earth beads (−2), giving 7.
3 3) Ten-complement (carry)
When you exceed 9, carry 1 to the left column and subtract the ten-complement from the current column. Example 8 + 5: since 5 = 10 − 5, add 1 to the tens and subtract 5 from the ones, giving 13.
Ejemplos interactivos
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