To make a cylindrical chimney with a bottom diameter of 40 cm and a height of 2 meters, at least how many square meters of iron sheet is needed.
做一个底面直径为40厘米、高是2米的圆柱形烟囱，至少需要铁皮多少平方米．
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3.14 * (2/5) * 2</gadget>
<output>2.512</output>

<result>2.512</result>