To find the area of the dining room, take 20m x 20m=400m
The area of each tile is 20cm x 20cm=40cm.
Convert the are of the dining room to cm which is 400 x 100= 40000cm
The divide the area of the dining room by the are of the tiles to find how m,any tiles are needed.
Which is 40000cm/40cm= 1000 tiles