To make 20 cylindrical iron chimneys, each chimney is 2.5 meters long, and the diameter of the cross section is 40 cm. How many square meters of iron sheets will be used in total?
做20节圆柱形铁皮烟囱，每节烟囱长2.5米，横截面的直径是40厘米，一共要用多少平方米的铁皮？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3.14 * (2/5) * 2.5 * 20</gadget>
<output>62.8</output>

<result>62.8</result>