In a ratio, the two outer terms are reciprocals of each other, one of the inner terms is (5/13), and the other inner term is how much.
在一个比例中，两个外项互为倒数，其中一个内项是(5/13)，另一个内项是多少．
<gadget id="calculator">5 / 13</gadget>
<output>5/13 = around 0.384615</output>

<gadget id="calculator">1 / (5/13)</gadget>
<output>13/5 = around 2.6</output>

<result>13/5 = around 2.6</result>