In the ratio, the product of two outer terms is 4, one inner term is (1/4), and the other inner term is how much.
在比例里，两个外项的积为4，一个内项是(1/4)，另一内项为多少．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">4 / (1/4)</gadget>
<output>16</output>

<result>16</result>