There are two red balls and several white balls in a box, if the possibility of drawing a red ball is (1/5), how many white balls should be put in.
一个盒子中有两个红球和若干个白球，要是摸出红球的可能性为(1/5)，则需放入多少个白球．
<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>