Counting with restrictions

A rule like these two cannot sit together changes the count. Two reliable moves: place the restricted objects first and fill in around them, or count everything and subtract the arrangements that break the rule.

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Work through it

LearnWhat it is, how to spot it, a worked example, and where it goes wrong.
Practice — 3-point ladderNo problems written at this tier yet.Nothing written at this tier yet
Practice — 4-point ladderNo problems written at this tier yet.Nothing written at this tier yet
Practice — 5-point ladder2 problems. Three in a row finishes it.0/3 in a row · 0/2 solved
Skill quizFinish every ladder that has problems first.Finish the ladders above first

Before and after

Needs first

CNT-05Arrangements of a few objects CNT-09Complementary counting

Opens up

Nothing yet. No other skill in the Atlas lists this one as a prerequisite.

In official papers

No indexed official paper question has been tagged with CNT-11 yet. The index grows one paper at a time, and it records only question numbers, point values and our own skill tags — never the problems themselves.

See the papers indexed so far

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