A and B work together to do a job, the part that A does accounts for B's (2/5), and the part that B does accounts for the whole work.
甲、乙合做一件工作，甲做的部分占乙的(2/5)，乙做的占全部工作的多少．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 + (2/5)</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">1 / (7/5)</gadget>
<output>5/7 = around 0.714286</output>

<result>5/7 = around 0.714286</result>