We have some real math maniacs in this house.
I saw a cute sign like this one in a Hallmark store last year and thought of them.
I almost bought it despite the $22.95 price tag. That seemed awfully steep.
So I made this for the cost of a canvas ($2 on sale at Hobby Lobby) and materials I had on hand - paint, rub-on letters, and a white paint marker.
The boys really love it :)