# Number magic - math puzzle

If you multiply me by 2, subtract 1, and read the reverse the result you'll find me. Which numbers can I be?

# Platonic solids - math puzzle

Show that there exist only five platonic solids (that are objects which are build out of the one sort of regular polygons, like the tetrahedron and the cube). Hint: use that for each solid in three dimensions it holds that the number of vertices + the number of faces is equal to the number of edges + 2. |