Change the denominator of (3/5) to 25, how much should be added to the numerator to keep the size of the fraction unchanged.
把(3/5)的分母变成25，要使分数大小不变，分子应加上多少．
<gadget id="calculator">25 / 5</gadget>
<output>5</output>

<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<result>12</result>