Case 23 · visual · Easy · About 4–6 minutes
Three museum volunteers prepared a paper display while the curator was away. Each placed one cutout, and the final arrangement appears in the evidence picture.
The curator needs to credit the volunteer who placed the triangle. The page does not show their names, but the placement rules and two register notes survive.
The placement rules
- Eleni, Finn, and Gray entered one at a time. Each entered once and placed exactly one of the three cutouts.
- The cutouts are one square, one circle, and one triangle.
- A newly placed cutout lay on top of any existing cutout it overlapped.
- No one slid a piece underneath another, lifted an earlier piece, or moved anything after placement.
The register notes
- Gray placed the circle.
- Eleni entered before Finn.
Picture evidence
Accessible evidence transcript: The circle overlaps the square and lies above it. The triangle overlaps the circle and lies above it. Enough of every cutout remains visible to identify its shape.
Who placed the triangle? Give all three volunteers’ shapes and the chronological order of their visits. Use the overlap relationships, rather than color, to recover the sequence.
The colors help distinguish the illustration’s surfaces, but the same logic works in monochrome. The size of a cutout does not indicate a volunteer’s age or importance. The case permits no hidden fourth visitor or rearrangement after the three visits.
Hint 1 - reveal when you want a nudge
A later piece must be above an earlier piece wherever they overlap.
Hint 2 - reveal when you want a nudge
The circle must be placed after the square and before the triangle. Gray therefore occupies the middle visit.
Reveal the solution and explanation
Finn placed the triangle. Eleni placed the square first, Gray placed the circle second, and Finn placed the triangle last.
Because the circle lies above the square, the square was placed first. Because the triangle lies above the circle, the triangle came afterward. Together, those relationships establish square → circle → triangle.
Gray’s circle fixes Gray in the middle. Eleni and Finn must occupy the first and last visits. The note that Eleni entered before Finn fixes Eleni first and Finn last.
There is no remaining choice of shapes or visit order. The conclusion depends on the stated rule against sliding pieces underneath one another. Without that rule, the same visible layers would not necessarily establish the history of placement.
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