There are five basic tetrominos, as seen above.
Can these seven pieces be placed into a 4x7 rectangle, to create a
checkerboard pattern? Reflections and rotations
are allowed.
Source: Original.
1. No. Consider coloring the grid and pieces as a checkerboard. The T-piece must cover three of one color and one of another. All other pieces cover 2 of each color, so the pieces cover 11 of one color and 9 of the other. The grid has 10 of each color, so cannot be covered.
2. With the corners black, there are 11 black and 10 white. The T-piece forces us to cover 11 of one color and 9 of the other. A white square will always be left uncovered.
3 & 4. See Kirk's powerpoint slides. Each of the puzzles has a solution.