The two internal terms of a ratio are (1/5), one of the external terms is (3/5), and the other external term is how much.
一个比例的两个内项都是(1/5)，其中一个外项是(3/5)，另外一个外项是多少．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(1/5) / (3/5)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/5) * (1/3)</gadget>
<output>1/15 = around 0.066667</output>

<result>1/15 = around 0.066667</result>