https://www.ck12.org/book/ck-12-middle-school-math-concepts-...
> An edge is the place where two faces meet. Edges are straight; they cannot be curved.
> Cones, spheres, and cylinders do not have any edges because they do not have any flat sides.
> An edge is the place where two faces meet. Edges are straight; they cannot be curved.
> Cones, spheres, and cylinders do not have any edges because they do not have any flat sides.
2. Any sharp terminating border; a margin; a brink; extreme verge; as, the edge of a table, a precipice.
4. The border or part adjacent to the line of division; the beginning or early part; as, in the edge of evening. "On the edge of winter." Milton.
Either the literal sense 2 or figurative sense 4 works here. The special mathematical sense is nowhere given in that edition of Webster's. I suppose they expected one would consult Euclid if one wished to know its sense in that jargon.
2.4 + 2.4 = 4.8, rounded is 5.
Therefore, 2 + 2 = 5.
I was taught this as a "mind teaser" in middle school once. It was supposed to be cute and fun, but just ended up confusing half the class.