7.The floor of a building consists of 3000 tiles which are rhombus shaped and each of its diagonals are 45 cm and 30 cm in length. Find the total cost of polishing the floor, if the cost per \(m^2\) is ₹ 4.

Given, number of tiles = 3000 and the length of the two diagonals of a tile = 45 cm and 30 cm
We have area of one rhombus shaped tile =\(\frac { 1 }{ 2 }\times d1 \times d2\)

\(=\frac { 1 }{ 2 }\times 45 \times 30\)

\(= 45 \times 15\)

\(= 675 cm^2\)

So, area of one tile=675\(cm^2\)

Therefore, Area covered by 3000 tiles = \(3000 \times 675 cm^2 = 2025000 cm^2 = 202.5 m^2\)

So, the cost of polishing the floor = \(202.5 \times 4 = ₹ 810\quad\)[∵ cost per \(m^2\) is ₹ 4. ]

Hence, the required cost = ₹ 810.