How many square meters of iron sheets are needed to make five cylindrical ventilation pipes with a bottom diameter of 4 decimeters and a height of 8 meters?
制作5个底面直径为4分米，高为8米的圆柱形通风管，至少要多少平方米的铁皮？
<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3.14 * (2/5) * 8 * 5</gadget>
<output>50.24</output>

<result>50.24</result>