Change the numerator of (20/30) to 12, what should be the denominator to keep the fraction size unchanged.
把(20/30)的分子变成12，要使分数大小不变，分母应变为多少．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">30 * (3/5)</gadget>
<output>18</output>

<result>18</result>