To make 50 iron rings with a diameter of 20 cm, at least how many meters of iron wire are needed.
要做直径是20厘米长的铁圈50个，至少需要铁丝多少米．
<gadget id="calculator">3.14 * 20 * 50</gadget>
<output>3_140</output>

<gadget id="calculator">3_140 / 100</gadget>
<output>157/5 = around 31.4</output>

<result>157/5 = around 31.4</result>