The length and breadth of the floor of the room are 20 feet and 10 feet respectively. Square tiles of 2 feet length of different colours are to be laid on the floor. Black tiles are laid in the first row on all sides. If white tiles are laid in the one-third of the remaining and blue tiles in the rest, how many blue tiles will be there ?

Area left after laying black tiles :
$$\eqalign{ & = \left[ {\left( {20 - 4} \right) \times \left( {10 - 4} \right)} \right]{\text{sq}}{\text{.ft.}} \cr & = 96\,{\text{sq}}{\text{.ft.}} \cr} $$
Area under white tiles :
$$\eqalign{ & = \left( {\frac{1}{3} \times 96} \right){\text{sq}}{\text{.ft.}} \cr & = 32\,{\text{sq}}{\text{.ft.}} \cr} $$
Area under blue tiles :
$$\eqalign{ & = \left( {96 - 32} \right){\text{sq}}{\text{.ft.}} \cr & = 64\,{\text{sq}}{\text{.ft.}} \cr} $$
Number of blue tiles :
$$\eqalign{ & = \frac{{64}}{{\left( {2 \times 2} \right)}} \cr & = 16 \cr} $$