In a ratio, the product of two outer terms is 4, one inner term is (4/5), and the other inner term is what.
在一个比例里，两个外项的积是4，一个内项是(4/5)，另一个内项是多少．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">4 / (4/5)</gadget>
<output>5</output>

<result>5</result>