I am not a "magician" by any means, but had been pretty good at math, algebra, etc.
The area of the rectangle changed with the additional pieces, but not its general shape. Note, that the ratio between the long and short side of the rectangle changed as well.With that change, the frame size's side ratio had to change as well to accommodate the rearranged shape of the rectangle.
The trick is a somewhat "flexible" frame, that extends/contracts, based on the number shapes in the rectangle. Designing this magician toy had probably been the hard part. Detecting the "trick" in this puzzle should not "puzzle" mathematicians for long. Pun intended...
The area of the rectangle changed with the additional pieces, but not its general shape. Note, that the ratio between the long and short side of the rectangle changed as well.With that change, the frame size's side ratio had to change as well to accommodate the rearranged shape of the rectangle.
The trick is a somewhat "flexible" frame, that extends/contracts, based on the number shapes in the rectangle. Designing this magician toy had probably been the hard part. Detecting the "trick" in this puzzle should not "puzzle" mathematicians for long. Pun intended...