The two inner terms of a ratio are 10 and (4/5), one outer term is 4, and the other outer term is how much.
一个比例的两个内项分别是10和(4/5)，一个外项是4，另一个外项是多少．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(4/5) / 4</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">10 * (1/5)</gadget>
<output>2</output>

<result>2</result>