Huangshan Machine Tool Factory wants to manufacture a batch of ventilation pipes. The cross section of the ventilation pipes is a square with a side length of 4 decimeters and a length of 2.5 meters. If 50 such ventilating pipes are made of iron sheets, how many square meters of iron sheets are needed?
黄山机床厂要制造一批通风管，通风管的横截面是边长是4分米的正方形，长2.5米．如果用铁皮做这样的通风管50只，需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">(2/5) * 4 * 2.5 * 50</gadget>
<output>200</output>

<result>200</result>