The Hinged Square and Other Puzzles

A colourful square, dissected into four parts, with hinges marked in black. If you leave the blue piece fixed and swing the others around their hinges, a new shape will emerge. Can you guess just by looking what it will be? This is just one of the tricky geometrical gems that will make a puzzler's mind work overtime. Try drawing a set of variously shaped polygons using only a compass and a ruler (no measuring allowed!); figuring out which of two sculptures is bigger (logic alone won't give you the answer); and lots more.