One Piece Fits
Read the puzzle
A hole is six squares: a row of four, one square above the second and one below the fourth. Pieces: A, a row of four, one square above the second, one below the third. B, a column of four, one square left of the top, one right of the third. C, a column of four, one right of the top, one left of the third. D, a column of four, one right of the top, one left of the bottom. May turn, never flip. Which piece fills the hole?
Pieces may turn but never flip over. Which piece fills the hole?
PIECE C
Turn C a quarter turn: it drops right in.
How to solve it
Describe the hole as a spine with bumps. Its spine is a row of four squares. One bump sticks up from the second square, and one hangs down from the fourth square, on the opposite side.
Describe each piece the same way. A has its lower bump under the third square, not the end square, so it fails. D has both bumps on the end squares of its spine, so it fails. B and C both have bumps on the first and third squares of a column, on opposite sides, so they match in pattern.
Now turn them. Rotate C a quarter turn clockwise: its column becomes a row, its top square becomes the right end, the square to the right of the top swings down below that end, and the square to the left of the third swings up above the second. That is exactly the hole, so C drops in.
The usual trap is B. B is the mirror image of C, so it would only fit if it were flipped over, which the rules forbid. Quick check: no amount of turning can change a left-handed shape into a right-handed one.
Learn the method: How to Solve Mental Rotation Puzzles: Turned or Mirrored?
