In a ratio, the two outer terms are exactly reciprocals of each other, one of the inner terms is 2, and the other inner term is how much.
一个比例里，两个外项正好互为倒数，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>