Find the perimeter of a rectangle having length of 8m 5dm and breadth of 6m 8dm.

Hint: To find the perimeter of the given rectangle, we have to use the formula $P=2\left( l+b \right)$ , where l is the length and b is the breadth of the rectangle. Firstly, we have to convert the meter measurements of length and breadth into decimeters by using the formula 1 meter is equal to 10 decimeters. Then, we have to substitute the values in the formula for the perimeter of a rectangle.

Complete step by step answer:
We have to find the perimeter of a rectangle having length of 8m 5dm and breadth of 6m 8dm. Let us first convert the units of length and breadth into decimeter. We know that 1 meter is equal to 10dm Therefore, we can write 8m as
$8\text{m}=8\times 10\text{dm}=80\text{dm}$
Therefore, we can write the given length (l) as
$\begin{align}
  & l=\text{8m 5dm} \\
 & \Rightarrow l=\left( 80+5 \right)\text{dm} \\
 & \Rightarrow l=85\text{dm} \\
\end{align}$
Now, let us consider the breadth (b). We can convert 6m into decimeters as follows.
$\begin{align}
  & 6\text{m}=6\times 10\text{dm} \\
 & \Rightarrow 6\text{m}=60\text{dm} \\
\end{align}$
Therefore, we can write the breadth as
$\begin{align}
  & \Rightarrow b=6\text{m 8dm} \\
 & \Rightarrow b=\left( 60+8 \right)\text{dm} \\
 & \Rightarrow b=68\text{dm} \\
\end{align}$
We know that perimeter of a rectangle with length, l and breadth, b is given by
$P=2\left( l+b \right)$

Let us substitute the given values of length and breadth in the above formula.
$\Rightarrow P=2\left( 85+68 \right)$
We have to add 85 and 68.
$\Rightarrow P=2\times 153$
Now, we have to multiply 153 by 2.
$\Rightarrow P=306\text{dm}$

Note: Students must note that the perimeter is in decimeters. They must never forget to write the units at the end of each measurement. Students should never get confused with the perimeter and area of a rectangle. The latter is given by
$A=l\times b$