To make a chimney with 10 sections with a base diameter of 20 cm and a length of 1 meter, at least how many square meters of iron sheets are needed.
做10节底面直径20厘米，长1米的烟囱，至少需要多少平方米的铁皮．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3.14 * (1/5) * 1 * 10</gadget>
<output>6.28</output>

<result>6.28</result>