Fly the flags

The penultimate Catriona Shearer puzzle.

19.
Fly the Flags

Squares of the same colour are the same size. What’s the total shaded area?

Spoiler!

The blue squares touch at the center and their edges are at 45° from the big squares’, so they lie on diagonals which we might as well draw:

at which point it’s obvious the red squares are 1/3 the size, 1/9 the area of the big square. Of course the diagonals of the blue squares are half the sides of the big square so they are each 1/8 the area. Total area is 36\times 2(1/9+1/8) = 17.

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