There are two yellow balls in the box. How many red balls need to be placed in order to make the probability of drawing a yellow ball (1/5).
盒子中有两个黄球．要使摸出黄球的可能性为(1/5)，还需要放入多少个红球．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">10 - 2</gadget>
<output>8</output>

<result>8</result>