How many tiles of measure 10 cm x 10 cm are required to cover a surface of 4m x 2.5 m?

Area of the surface = 2.5 m $\times$ 4 m = 10 m² = 10 $\times$ 10000 = 100000 cm²
area of each tile = 10 cm $\times$ 10 cm = 100 cm²
no. of tiles  = $\frac{area of surface}{area of each tile} = \frac{100000}{100} = 1000$$\frac{area of surface}{area of each tile} = \frac{100000}{100} = 1000$