DAY 69

Comment

If, for example, tile A is removed, 3 edges are lost but 1 new edge is exposed (so the perimeter decreases by 2 edges).
If E is removed, 1 edge is lost but 3 new edges are exposed, so the perimeter increases by 2 edges).
For which tile is the number of edges lost the same as the number of new edges exposed?

Answer

Removing tile D does not change the size of the perimeter.

Readers' methods

Katjia Berend, Linz:
Think of the tiles as 1 cm squares.
Then if tile D is removed, 2 cm of the perimeter is removed, but another 2 cm is revealed.

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