A lane 150 m long and 9 m wide is to be paved with bricks, each measuring 22.5 cm by 7.5 cm. How many bricks are required ? HINT : $\text{Area of the lane}$ $=(150 \times 100 \times 9 \times 100) cm ^2$. $\quad\quad~~\text { Area of each brick }=\left(\frac{225}{10} \times \frac{75}{10}\right) cm^2.$ $\quad\quad~~\text { Number of bricks }=\left(150 \times 100 \times 9 \times 100 \times \frac{10}{225}\times\frac{10}{75}\right)=80000.$
A room is 5 m 40 cm long and 4 m 50 cm broad. Its area is HINT : $\text { Area }=(5.4 \times 4.5) m^2=\left(\frac{54}{10} \times \frac{45}{10}\right) m^2=24.3 m^2.$
If the ratio between the length and perimeter of a rectangular plot is 1 : 3 then the ratio between the length and breadth of the plot is HINT : Let the length be $x$ cm. Then, its perimeter is 3$x$ cm. $\quad\quad~~\therefore 2(x+b)=3 x \Rightarrow x+b=\frac{3 x}{2} \Rightarrow b=\left(\frac{3 x}{2}-x\right)=\frac{x}{2}$. $\quad\quad~~\therefore l: b=\left(x: \frac{x}{2}\right)=(2 x: x)=2: 1$.
The length of a rectangle is three times its width and the length of its diagonal is $6 \sqrt{10}$ cm. The perimeter of the rectangle is HINT : Let width be $x$ cm. Then, length = 3$x$ cm. $\quad\quad~~\therefore \sqrt{x^2+9 x^2}=6 \sqrt{10} \Rightarrow 10 x^2=360 \Rightarrow x^2=36 \Rightarrow x=6$.