To calculate the number of tiles needed for a 7-meter by 3-meter area using 20*100 tiles, follow these steps:
Calculate the total area in square meters: Area = Length * Width = 7 meters * 3 meters = 21 square meters
Calculate the area covered by each tile in square meters: Tile area = Length of tile * Width of tile = 20 cm * 100 cm = 0.2 meters * 1 meter = 0.2 square meters
Divide the total area by the area covered by each tile to get the number of tiles needed: Number of tiles = Total area / Tile area = 21 square meters / 0.2 square meters = 105 tiles
You would need 105 tiles of size 20 cm * 100 cm to cover a 7-meter by 3-meter area. Keep in mind that it's a good idea to purchase a few extra tiles in case of breakage or future repairs.