Notes
stacked squares inside two squares solution

Solution to the Stacked Squares Inside Two Squares Puzzle

Stacked Squares Inside Two Squares

The purple squares are all the same size. I’ve arranged three of them symmetrically inside each of the two black squares. What’s the missing length?

Solution by Lengths in Squares

Stacked squares inside two squares labelled

Let xx be the side length of one of the purple squares. So ABA B and DED E both have length xx. The diagonal of the square is then 2x\sqrt{2} x, so that is the length of GFG F. Let yy be the length of BCB C, then this is also the length of CFC F. Then the width of the square is 2x+2y2 x + 2 y and the height is x+2xyx + \sqrt{2} x - y. As it is a square, these are both equal to 1212. The length requested is 2x+2x2 x + \sqrt{2} x which can be seen to be equal to:

2x+2x=x+2xy+x+y=12+6=18. 2 x + \sqrt{2} x = x + \sqrt{2} x - y + x + y = 12 + 6 = 18.