In a ratio, the two outer terms are exactly reciprocals of each other, one of the inner terms is 0.5, and the other inner term is how much.
在一个比例里，两个外项正好互为倒数，其中一个内项是0.5，另一个内项是多少．
<gadget id="calculator">1 / 0.5</gadget>
<output>2</output>

<result>2</result>