A part is 20cm long drawn on the diagram with a scale of 50:1, what is the actual length of the part in millimeters?
一个零件以比例尺50：1画在图上是20cm长，则这个零件的实际长度是多少毫米．
<gadget id="calculator">50 / 1</gadget>
<output>50</output>

<gadget id="calculator">20 / 50</gadget>
<output>2/5 = around 0.4</output>

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

<result>4</result>