Only whole tiles are used. How many tiles are neither diagonal tiles nor edge tiles?
If there are 121 tiles and both tiles and floor are square, this means there are 11 by 11 tile used on the floor (square root of 121 is 11) So if we exclude the edges, this means we have 9 by 9 tiles And there are 9 tiles on each diagonal but the one in the center is shared so we have total of 9+9-1=17 tiles on diagonals of this inner tiles with 9 by 9 So for 9 by 9 tiles we have 9x9=81 tiles and excluding 17 tiles on diagonals; the answer is 81-17=64 tiles.
