Here’s a problem that I heard from Gordon Hamilton at Gathering for Gardner 9, and tracked down to an article of his in issue #10 of Pi in the Sky, a western Canadian math magazine for high school students and teachers.
A polyomino animal can eat another polyomino animal (his perhaps overly cute term is “polyanimal”) if the second one can be placed inside the first. Find animals of sizes 4, 5, 6, 7, 8, 9, and 10 that can live together peacefully (none can eat any of the others) within a 7×7 square pen.
This is really a satisfying puzzle to solve. Usually in polyform tiling puzzles, you spend a fair amount of time feeling out the territory, learning which pieces like to go in certain places, and which you want to deal with first and which you want to save for the end. But then, the larger part of the solving time is spent in trial and error with various configurations attempted at random until at last you run into a solution.
Here, the whole solving process is learning about the territory of the puzzle, and none of it feels like random crunching. I highly recommend giving it a try, but if you just want to see a solution, mine is here.
Of course, the matter of polyominoes fitting inside other polyominoes is an area that I’ve dealt with in my Polyomino Cover material, which I summarized in my presentation for G4G9. And one of the problems in Hamilton’s Polyanimal problem set is the same as what I’ve called the minimal pentomino cover problem. But most of them are completely different, which only reinforces my belief that this is an area with a lot more waiting to be discovered. (His last problem is “Design a Polyanimal Game.” Now that’s open-ended and provocative!)