On a drawing with a scale of 10:1, the length of a part is measured as 4 cm, how many millimeters is the actual length of this part?
在一个比例尺是10：1的图纸上，量得一个零件的长是4厘米，这个零件实际长多少毫米
<gadget id="calculator">10 / 1</gadget>
<output>10</output>

<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

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

<result>4</result>