Half a Turn
Read the puzzle
A square card shows a 3 by 3 grid of cells, gold (1) or dark (0), with a cut top-right corner. Rows, top to bottom: 111, 100, 001. The card is given a half turn (rotated 180°), not flipped. Which card do you get? A: 111, 001, 100. B: 111, 100, 001. C: 001, 100, 111. D: 100, 001, 111.
Which card do you get?
Turn the card 180°, do not flip it.
D
Rotate 180°: the top row lands at the bottom, reversed. Card D.
How to solve it
A half turn sends every cell to the opposite position: the top row becomes the bottom row and is read backwards, and the left side swaps with the right.
Take the rows one at a time. The top row is all gold, so the new bottom row is all gold. The middle row is gold on the left, so after the turn it is gold on the right. The bottom row is gold only on the right, so it becomes the top row with gold only on the left.
Result: top left gold, middle right gold, bottom row all gold. That is card D.
The common wrong pick is C. It also has a full bottom row, but its other cells stay on their original sides, so it is a top-to-bottom flip, a mirror image, not a turn. A is a left-to-right flip, and B is the card unchanged.
Quick check: the cut corner starts at the top right, so after a half turn it sits at the bottom left. The lone gold cell at the bottom right must end up at the top left, and only D has that together with a full bottom row.
Learn the method: How to Solve Mental Rotation Puzzles: Turned or Mirrored?
