To make a ventilation pipe with a bottom diameter of 25 cm and a length of 8 cm, at least how many square decimeters of iron sheet are needed.
做一节底面直径是25厘米，长8厘米的通风管，至少需铁皮多少平方分米．
<gadget id="calculator">3.14 * 25 * 8</gadget>
<output>628</output>

<gadget id="calculator">628 / 100</gadget>
<output>157/25 = around 6.28</output>

<result>157/25 = around 6.28</result>