A circle is surrounded by an iron wire, and the radius is exactly 5 decimeters. If this iron wire is changed into a square, what is the length of its side?
用一根铁丝围成一个圆，半径正好是5分米，如果把这根铁丝改围成一个正方形，它的边长是多少分米．
<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">3.14 * 5 * (1/2)</gadget>
<output>7.85</output>

<result>7.85</result>