If there is a largest circle inside a square with a side length of 20 cm, what is the area of this circle in the area of the square?
一个边长20厘米的正方形内有一个最大的圆，这个圆的面积占正方形面积的多少．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<gadget id="calculator">314 / 400</gadget>
<output>157/200 = around 0.785</output>

<result>157/200 = around 0.785</result>