Question

The perimeter of a rectangle is $40$ cm and if one of the side has a length of $8$ cm, then the length of the other side (in cm) is:

• A. 12

Answer 1

The correct option is A 12

Given the perimeter of the rectangle $ABCD=40$ cm
And one of the side has a length $l_2=8$ cm.
Let ${}^{\prime }{k}^{\prime }$ be the length of the unknown side.
Now, we know perimeter of a rectangle $=2\times (l_1+l_2)$
$\Rightarrow 40=2\times (k+8)$
Dividing both sides by $2$:
$\Rightarrow \frac{40}{2}=\frac{2\times (k+8)}{2}$
$\Rightarrow 20=k+8$
Now, subtracting $8$ on both sides:
$\Rightarrow 20-8=k+8-8$
$\Rightarrow 12=k$
Or $k=12$ cm.
$\therefore$ The length of the unknown side is $12$ cm.