Variable As Unknown
Variable As Unknown practice with teacher guidance, common slips, and next-step routes.
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Print: Ages 10–11 · 5–9 min · Challenge · Constraints Elimination · Independent practice · Digit Assignment
Watch: Watch whether the learner tests both possible ones-column pairs before choosing. Decisive evidence is showing that both cases use the same six assigned digits, rather than presenting one valid equation.
Misread: Choosing 2, 4, 5, or 6 usually means the learner stopped after one case or counted only some letter positions. Saying 0, 8, or 9 aloud shows they missed “besides,” even though those digits are not offered.
Curriculum: This task uses base-10 place value and carrying, all-different constraints, proof by cases, and set complement. It scores proving the invariant extra unused digit, not finding one letter-to-digit mapping.