The two outer terms of a ratio are reciprocals of each other, one of the inner terms is (2/9), and the other inner term is what.
一个比例的两个外项互为倒数，其中一个内项是(2/9)，另一个内项是多少．
<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>