Perimeter of a rectangle

Let the shorter side of the rectangle be $a$ . Then the longer side is $2a$ . Therefore, the area of the rectangle is $A = 2a^2 = 50 \implies a^2 = 25 \implies a = 5$ . The perimeter of the rectangle is $p = 2(a+2a) = 6a = 6(5) = \boxed{30}$ .

Let $l$ be the longer side and $w$ be the shorter side, then we have

$50=lw$ $\color{#D61F06}\implies$ $\boxed{1}$

$\dfrac{w}{l}=\dfrac{1}{2}$ $\color{#D61F06}\implies$ $\boxed{2}$

From these $2$ equations we get: $w=5$ and $l=10$ . So the perimeter is $10+10+5+5=\color{#3D99F6}\boxed{30}$