It takes (1/5) hour for A and (1/4) hour for B to complete a job, how long will it take for A and B to finish it together?
完成一件工作，甲要(1/5)小时，乙要(1/4)小时，甲乙合做要多少时完成．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / (1/4)</gadget>
<output>4</output>

<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<result>1/9 = around 0.111111</result>