To make 20 sections of metal ventilation pipes, with a height of 3 meters and a bottom diameter of 20 cm, how many square meters of metal sheets are needed at least? (neglected at joints)
要制作20节铁皮通风管，高3米，底面直径20厘米，至少需要铁皮多少平方米？(接头处忽略不计)
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3.14 * (1/5) * 3 * 20</gadget>
<output>37.68</output>

<result>37.68</result>