On a drawing with a scale of 30:1, the length of a part on the drawing is 12 cm. What is its actual length in mm? (Solve with ratio)
在一幅比例尺是30：1的图纸上，一个零件的图上长度是12厘米，它的实际长度是多少毫米？(用比例解)
<gadget id="calculator">12 / 30</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) * 10</gadget>
<output>4</output>

<result>4</result>