1. The problem statement, all variables and given/known data We are using a drawing program in computer and we place x number of identical equilateral triangles(of same length of edges) randomly. So whenever we choose a triangle on the screen randomly(each has an equal number of possibility of being selected), we can slide the other triangles(without rotating them) in any way to cover the chosen one. In order to able to do this for each chosen triangle and for each different placements of the other triangles, what is the minimum number of triangles,that is x, placed on the screen? 2. Relevant equations 3. The attempt at a solution This problem is neither homework nor coursework; it is a challenging - i think -math puzzle i saw on the internet. I didn't solve it formally but i guess that the minimum number of triangles is 4 using the symmetry(both relative and intrinsic) of the equilateral triangles.