We want to put tiles in a new room. When they'll be laid, the room's floor will be a 5 by 5 square.
What operation has to be done to find the number of tiles that have to be taken to this room ?

If you think it's 5+5 take the yellow door;
If you think it's 5x5 take the red door;
If you think it's 5-5 the green door.