Add 10 to the denominator of (2/5), how much should the numerator be multiplied to keep the size of the fraction constant
把(2/5)的分母加10，要使分数的大小不变，分子应当乘多少
<gadget id="calculator">5 + 10</gadget>
<output>15</output>

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

<result>3</result>