Pentominoes
Tap a piece, then tap the board to put it down. Use Turn and Flip to change the way it faces. Tap a piece on the board to pick it up again. The goal: fit all twelve pieces into the rectangle with no gaps and no overlaps.
What's going on
A pentomino is a shape made of five squares joined edge to edge. If a shape turned round or flipped over counts as the same shape, there are exactly twelve of them. People name them after the letters they look like: F, I, L, N, P, T, U, V, W, X, Y and Z.
Twelve pieces of five squares cover 12 × 5 = 60 squares. So they might fill any rectangle with area 60: 6 by 10, 5 by 12, 4 by 15 or 3 by 20. They can fill all four, but it is hard. The 6 by 10 board has 2,339 different answers and the 3 by 20 board has only 2.
A tip: place the awkward pieces first. The X needs room on all four sides, and the I, W and F leave odd gaps. Save the P for last, because it fits almost anywhere. And watch for a gap of one, two, three or four squares that is walled in. No piece is that small, so a gap like that means something has to move.
The Hint button puts one piece where it belongs in an answer the demo knows. It may move pieces that are in its way.
Sheet: The twelve pentominoes. Related demo: Will it fold?