A rectangular garden of dimension 12m by 9m is enclosed by a uniform concrete walk 1.5m wide. If the walk is to be tiled, how many 30cm- square tile are needed to tile the entire walk?
The area of the walk is 15*12 - 12*9 = 72m^2
72m^2 / (.3m)^2 = 800 tiles
Or, you can figure 5 tiles to cross the width of the walk. The garden is 12/.3 = 40 tiles long and 9/.3 = 30 tiles wide.
You will need
two strips of 40x5 on the long side
two strips of 30x5 on the short side
4 corners of 5x5
400+300+100 = 800