Cut out the largest circle from a square iron sheet with a side length of 40 cm. By what percentage is the area of the circle reduced from the area of the square?
从一张边长为40厘米的正方形铁皮上剪下一个最大的圆，圆的面积比正方形的面积减少了百分之几？
<gadget id="calculator">40 * 40</gadget>
<output>1_600</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 ** 2</gadget>
<output>400</output>

<gadget id="calculator">3.14 * 400</gadget>
<output>1_256</output>

<gadget id="calculator">1_600 - 1_256</gadget>
<output>344</output>

<gadget id="calculator">344 / 1_600</gadget>
<output>43/200 = around 0.215</output>

<result>43/200 = around 0.215</result>