Asked in PPSC, FPSC and other one-paper exams (compiled from unofficial resources).

The length and breadth of the floor of a 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 on one-third of the remaining area and blue tiles on the rest, how many blue tiles will be there?

1. A.$12$
2. B.$16$Correct answer
3. C.$20$
4. D.$24$