Try the following GRE quantitative reasoning question that tests your understanding of the relationship between the diameter and area of a circular region.
Question#96:
$$ d = k \sqrt{\dfrac{A}{\pi}} $$
The formula above gives the diameter $d$ of a circular region in terms of its area $A$, then $k=$

$\quad 4$

$\quad 2$

$\quad 1$

$\quad \dfrac{1}{2}$

$\quad \dfrac{1}{4}$