Buy one or get all four.
Students in math just looove to not show you their work. I put these 4 posters up in each corner of my room. I use these posters when I come by a student’s desk to look at homework or classwork and I find they have NOT shown their work.
I point to one of the corners of the room where the poster is hanging and ask "What does that say?" Then I point to the next corner and repeat "What does that say?” I do this two more time pointing to each corner. When I've done this 4 times I finally ask "What do YOU think I want you to do?"