There are 30 people in the mathematics interest group, of which 40% are boys, how many are girls?
数学兴趣小组共有30人，其中男生占40%，女生有多少人．
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">30 * (3/5)</gadget>
<output>18</output>

<result>18</result>