If 3 is the middle term in the ratio of x and (1/2), then x=how much.
如果3是x和(1/2)的比例中项，那么x=多少．
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

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

<gadget id="calculator">9 / (1/2)</gadget>
<output>18</output>

<result>18</result>