Final answer:
The number of tiles needed to cover the kitchen wall is 1 tile.
Step-by-step explanation:
The area of the kitchen wall is given by the product of its length and width, which is 10m x 40m = 400m².
The area of each tile is the product of its sides, which is 20m x 20m = 400m².
To calculate the number of tiles needed to cover the wall, we divide the area of the wall by the area of each tile. Therefore, the number of tiles needed is 400m² / 400m² = 1 tile.