cylindrical ventilation pipe with a base radius of 5 cm and a length of 8 decimeters. How many square decimeters of iron sheet is needed to make a section of such ventilation pipe at least?
一个圆柱形通风管，底面半径5厘米，长8分米．做一节这样的通风管至少薷要铁皮多少平方分米？
<gadget id="calculator">5 / 10</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">3.14 * (1/2) * 2 * 8</gadget>
<output>25.12</output>

<result>25.12</result>