Girls' (2/5) is equivalent to boys' (2/7), how much more boys than girls.
女生的(2/5)相当于男生的(2/7)，男生比女生多多少．
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/7) / (2/5)</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">1 - (5/7)</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(2/7) / (5/7)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>