One piece of work, A needs (1/4) hour to finish, B needs (1/5) hour to finish, how many hours will it take A and B to finish together.
一件工作，甲要(1/4)小时完成，乙要(1/5)小时完成，甲乙合做要多少小时完成．
<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">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

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

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

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