The radius of the hoop is 25 cm. How many meters of wire are needed to make 20 such hoops?
铁环的半径是25厘米，如果要制作20个这样的铁环，需要多少米铁丝？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3.14 * 2 * 25 * (1/5)</gadget>
<output>31.4</output>

<result>31.4</result>