The numerator of (2/5) is increased by 8, how much should the denominator be increased to keep the size of the fraction constant.
(2/5)的分子增加8，要使分数的大小不变，分母应增加多少．
<gadget id="calculator">5 * 5</gadget>
<output>25</output>

<gadget id="calculator">25 - 5</gadget>
<output>20</output>

<result>20</result>