How many 20" tiles is needed for a 1200 square feet room
20 inches = 5/3 feet
so each tile is 25/9 square feet
number of tiles = 1200 / (25/9)
= 432
or
each tile = 400 square inches
1200 ft^2 = 172800 inches^2
number of tiles = 172800/400 = 432