In a ratio, the two inner terms are reciprocals of each other, one of the outer terms is (1/4), and the other is how much.
在一个比例里，两个內项互为倒数，其中一个外项是(1/4)，另一项是多少．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / (1/4)</gadget>
<output>4</output>

<result>4</result>