In the ratio, the two internal terms are reciprocals of each other, one of the external terms is 0.4, and the other external term is how much.
在比例里，两个内项互为倒数，其中一个外项是0.4，另一个外项是多少．
<gadget id="calculator">1 / 0.4</gadget>
<output>2.5</output>

<result>2.5</result>