In the ratio, the two outer terms are reciprocals of each other, one of the inner terms is (2/5), and the other inner term is how much.
在比例中，两个外项互为倒数，其中一个内项是(2/5)，另一个内项是多少．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / (2/5)</gadget>
<output>5/2 = around 2.5</output>

<result>5/2 = around 2.5</result>