Make a ventilation pipe with a length of 4 meters and a diameter of 10 cm. At least how many square meters of white iron sheet is used to make two ventilation pipes.
用铁皮做一根长4米的通风管，管口的直径是10厘米．做2个通风管至少要用白铁皮多少平方米．
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">3.14 * (1/10) * 4 * 2</gadget>
<output>2.512</output>

<result>2.512</result>