In a ratio, the two internal terms are reciprocals of each other, one external term is (7/9), and the other external term is how much.
在一个比例里，两个内项互为倒数，一个外项是(7/9)，另一个外项是多少．
<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">1 / (7/9)</gadget>
<output>9/7 = around 1.285714</output>

<result>9/7 = around 1.285714</result>