In the ratio, the two outer terms are reciprocals of each other, one inner term is 0.4, and the other inner term is what.
在比例中，两个外项互为倒数，一个内项是0.4，另一个内项是多少．
<gadget id="calculator">1 / 0.4</gadget>
<output>2.5</output>

<result>2.5</result>