(1/2): 4=(1/10): x.
(1/2)：4=(1/10)：x．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/10) / (1/2)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">4 * (1/5)</gadget>
<output>4/5 = around 0.8</output>

<result>4/5 = around 0.8</result>