1
Read the shape
Look for digit and factor structure. GCD (small, ≤ 30).
Level 9 - foundation
6 visual blocks - structure tests
Look for digit and factor structure. GCD (small, ≤ 30).
Use divisibility, remainders, GCD, or LCM.
Run the cheapest test first.
Use GCD x LCM = product when relevant.
Use the quickest safe method.
Do not trial-divide every number.
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