A ratio is 8:20=0.2:0.5. If you add 4 to the first item from left to right, how much should the second item be? The proportional formula still holds.
一个比例为8：20=0.2：0.5，如果从左往右第一项加4，那么第二项应为多少时比例式仍然成立．
<gadget id="calculator">8 + 4</gadget>
<output>12</output>

<gadget id="calculator">12 / 8</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">20 * (3/2)</gadget>
<output>30</output>

<result>30</result>