In a ratio, the two outer terms are reciprocals of each other. One of the internal items is 2, and the other internal item is how much.
在一个比例里，两个外项互为倒数．其中一个内项是2，另一个内项是多少．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>