When a is equal to how much, the fraction (4/(a)) and 4 are reciprocals of each other.
当a等于多少时，分数(4/(a))和4互为倒数．
<gadget id="calculator">4 / 1</gadget>
<output>4</output>

<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<result>16</result>