Add 10 to the numerator of (2/5), how much should be added to the denominator to keep the fraction constant.
(2/5)的分子加上10，要使分数大小不变，分母应加上多少．
<gadget id="calculator">2 + 10</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">5 * 6</gadget>
<output>30</output>

<gadget id="calculator">30 - 5</gadget>
<output>25</output>

<result>25</result>