A cube goes with the number 12, because a cube has 12 edges. Following that same idea, which number goes with a pyramid that stands on a square base?

A pyramid on a square base has 4 edges forming the square at the bottom and 4 more edges running up from the corners of that square to the apex, so 4 + 4 = 8 edges. The traps: 5 is the number of its faces (and also of its corners), the two counts most often confused with edges; 6 is the number of faces of a cube, borrowed from the wrong solid; 10 comes from counting the 4 base edges twice over.