Cut the largest circle from a square plastic sheet with a side length of 80 cm, and then put a circle of colored ribbons around the circle. At least how many meters of ribbon is needed?
从一块边长为80cm的正方形塑料片上截下一个最大的圆，再在圆的四周围上一圈彩带．至少需要彩带多少米？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">3.14 * (4/5)</gadget>
<output>2.512</output>

<result>2.512</result>