A square iron sheet has a circumference of 80 cm, and the largest circle is to be cut out. What is the diameter of this circle in cm?
一块正方形铁皮，周长是80cm，要剪下一个最大的圆，这个圆的直径是多少cm．
<gadget id="calculator">80 / 4</gadget>
<output>20</output>

<result>20</result>