NumihanaSoroban complements to five.
Add five with the upper bead, then remove the complement from the lower beads. A real soroban has one upper bead worth five and four lower beads worth one on each rod; only beads towards the bar count.
Recommended order: set numbers, read numbers, direct addition, direct subtraction, complements to five, complements to ten, then carrying. Removing a complement to ten can also require the complement-to-five technique.
When this helps
Optional enrichment for understanding place value and addition/subtraction. This is not a statutory teaching method.
A common slip
Only count beads touching the centre bar. The tens rod is ten times the ones rod, and an inactive upper bead contributes zero.
Worked example
3 + 4 = 7
Each upper bead is worth five; each lower bead is worth one. Active beads touch the centre bar. Read tens on the left and ones on the right.
Bead value: 7
First represent the starting number.
Set the two rods to the first quantity.
3What is the complement of 4 to five?
Work out 5 minus the amount being added. Add five, then remove this complement.
1What is the final answer?
Recombine your working and check it against the original question.
7
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Teaching context
This lesson practises mathematical representations and calculations. The displayed practice uses selected England Year 2 skills; the strategy can also help learners in other years.
Curriculum alignment describes the mathematical skill. It does not mean this is the only required teaching method.
Department for Education: mathematics programmes of study ↗Original method lesson v1.
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