Make a rectangular ventilation pipe with a height of 25 cm, a length and a width of 5 cm, and paint its exterior. If 0.4 kg of paint is applied per 1 square meter, how many kilograms of paint will be used to paint this ventilation pipe?
做一个高25厘米，长和宽都是5厘米的长方形通风管，把它的外表涂上油漆，如果每1平方米涂油漆0.4千克，涂这个通风管共要用油漆多少千克？
<gadget id="calculator">25 / 10_000</gadget>
<output>1/400 = around 0.0025</output>

<gadget id="calculator">5 * 5 * 4 * (1/400)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) * 0.4</gadget>
<output>0.1</output>

<result>0.1</result>