Two people, A and B, work together to do a job, the part that A does is accounted for (4/5) of B, and the part that B does is accounted for the whole work.
甲、乙二人合做一件工作，甲做的部分占乙的(4/5)，乙做的占全部工作的多少．
<gadget id="calculator">4 / 5</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>