A kitchen floor is to be tiled in the following way,
If the kitchen measures 15 tiles x 25 tiles, how many white tiles will be needed?
The floor is made up of a 2x2 repeating pattern,
A 15 25 floor will fit 7x12 repeating blocks (14x24 tiles). The "end" lines will be all white.
So there will be 7 12 = 84 grey tiles.
Hence there will be 15 25 84 = 374 84 = 291 white tiles.
What about a kitchen measuring m n tiles?