Black-cell number islands
Shade cells so surviving numbers do not repeat in any row or column, black cells never share an edge, and white cells stay connected.
Logic & rule checking · Shape & spatial thinking
- Players
- 1–4 cooperative
- Time
- 12–20 minutes
- Materials and quantities
- One numbered 4×4 puzzle and pencil. Optional large dark paper squares.
1–4 cooperative
Prepare
Copy the supplied four-by-four numbers exactly. A shaded number is removed from consideration. An unshaded cell keeps its printed number. Diagonal contact is allowed between black cells; only a shared edge is forbidden.
Solve
Choose cells to shade. After each choice check three independent rules: each row and column has no repeated surviving value; no two shaded cells share an edge; all remaining white cells can reach one another through up/down/left/right white cells. Numbers in different rows and columns may match.
Example
For a row 2,2,3,4, at least one of its two 2s must be shaded, but this local choice alone does not decide the puzzle. Check the corresponding columns and whether a white region becomes cut off. Do not treat diagonal white contact as a route.
Finish
A solution must satisfy all three rules at once. The teacher page gives one checked solution, not a claim of uniqueness; another fully checked valid shading is accepted. Write down the shaded coordinates and explain connectivity before comparing keys.
Adapt
Use removable large paper markers before committing pencil marks. One partner checks duplicates and another traces white connectivity. Begin with a single row to understand removal, but do not call that a full-board solution.
Aim: Shade cells so surviving numbers do not repeat in any row or column, black cells never share an edge, and white cells stay connected.
Practice within this activity: Shade cells so surviving numbers do not repeat in any row or column, black cells never share an edge, and white cells stay connected.
Adult observation: Ask the participant to explain one legal choice. Accept passing and a partner writing; do not infer a lasting ability from a single round.
Mechanism and adaptation: A separately written PartyPageKit version of the mechanism described below, with original examples and materials. The earliest inventor is not established here.
Goals describe observable activity choices, not measured long-term gains or institutional endorsement.
Free alternatives: Hand-copy the small number grid on reused paper and mark a black cell with a large X.
Buying recommendations reserved; no purchase required.
Printable materials
Preview at 100% scale, with browser headers and footers off. Cut with suitable help. Keep host keys separate. This is a manual tabletop kit, not an online opponent, automatic judge or solver.
Player number island puzzle
Shade to remove duplicates in each row/column. Black cells may not share an edge; all white cells must connect by edges.
Solution-check log
| Shaded cells | Rows/columns distinct? | Black adjacency? | White connected? |
|---|---|---|---|
| ________ | ________ | ________ | ________ |
| ________ | ________ | ________ | ________ |
| ________ | ________ | ________ | ________ |
| ________ | ________ | ________ | ________ |
Teacher instructions and checked example · separate
1–4 cooperative
One numbered 4×4 puzzle and pencil. Optional large dark paper squares.
Hand-copy the small number grid on reused paper and mark a black cell with a large X.
Print only the relevant player pages; keep this teacher page separate. Read the full web rules before leading. A helper may write or move pieces, and anyone may pause or pass. No classroom or physical-printer trial is claimed.
One valid answer shades A1, C3, D4. Shaded cells touch no edge; remaining white cells form one edge-connected region, with distinct surviving values in each row and column. Other fully checked answers are allowed.