The number of boys is 80% of the number of girls, and the number of girls accounts for the number of the whole class.
男生人数是女生的80%，女生人数占全班的多少．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 + (4/5)</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">1 / (9/5)</gadget>
<output>5/9 = around 0.555556</output>

<result>5/9 = around 0.555556</result>