The number of girls in Class 1 is reduced by 20%, which is equal to the number of boys. The number of boys in this class is equal to the number of girls
六1班女生人数减少20%，就和男生人数相等，这个班中男生人数是女生人数的多少
<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>

<result>4/5 = around 0.8</result>