There are 25 girls in a class, and boys are 20% less than girls. How many boys are there?
一班有女生25人，男生比女生少20%．男生有多少人．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">25 * (4/5)</gadget>
<output>20</output>

<result>20</result>