Question

# A $5$ meter wide lane was paved with bricks of size $20\text{ }cm\text{ }\times \text{ }15\text{ }cm$ . If the rate of bricks is $Rs.750$ per $1000$ and if the bricks worth $Rs.49500$ were used for pavement, find the length of the lane.

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Hint: Here we use the concept of area of the rectangle.
Area of rectangle = length $\times$ breadth

$Rs.750$ represents the cost of $1000$ bricks.
$Rs.49500$ represents cost of ? bricks, which represents the total number of bricks used.
\begin{align} & \dfrac{Total\text{ }\cos t\text{ }of\text{ }used\text{ }bricks}{\cos t\text{ }of\,1000\text{ }bricks}\times 1000\text{ }bricks \\ & =\dfrac{49500}{750}\times 1000 \\ & =66000 \\ \end{align}
The total number of bricks used is $66000$.
\begin{align} & Area\text{ }of\text{ }lane=total\text{ n}umber\text{ }of\text{ }bricks\times area\text{ }of\text{ }each\text{ }brick \\ & \Rightarrow l\times 5m=66000\times (20cm\times 15cm) \\ & \Rightarrow l=\dfrac{66000\times (20cm\times 15cm)}{5m} \\ & \Rightarrow l=\dfrac{66000\times (20cm\times 15cm)}{500cm} \\ & \Rightarrow l=39600cm \\ & \Rightarrow l=396m \\ \end{align}
Therefore, length of lane is $396\,m$.