← Pattern Anatomy

Pattern Anatomy

Each pattern, deconstructed.

modular-cycle-frequency-count

Rank 10/19 2.0% of all AMC problems Grade 4–6

A sequence (often arithmetic, sometimes a schedule of dates) is distributed across residue bins modulo m, and the problem asks which residue is missing, which bin has the most or fewest, or which histogram matches. The decisive move is recognizing that the period m gives a uniform "base" count over a full cycle and a tail correction over the leftover entries.

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27-year frequency
1999–2026 ↑ 150%
2026 forecast slots

How to solve

Primary tools find-patternssimplifymath-tools
What to look for
  • Swap modulus 7 (days of week) for modulus 5 (school days) or modulus 12 (months) — the cycle bookkeeping is structurally the same
  • Replace 'which histogram matches' with 'which residue never appears' to force the same reasoning without picture options
  • Use a non-uniform tail (e.g. last few entries land in a specific cluster) to make the +1 correction step the load-bearing move

Sub-archetype mix (4)

Click a row to see member problems.

More data (year-over-year, tool fingerprint, grade distribution, all members)
18
members
1999–2026
Active years
Year-over-year

Tool fingerprint (1–17)

Grade distribution

  • Gr 4
    7
  • Gr 5
    3
  • Gr 6
    6
  • Gr 8
    2