A task can be completed by A alone in 8 hours and B alone in 10 hours, how many hours the two work together will leave (1/10) of the project.
一项任务，甲单独做8小时完成，乙单独做10小时完成，两人合做多少小时还剩下这项工程的(1/10)．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 - (1/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/8) + (1/10)</gadget>
<output>9/40 = around 0.225</output>

<gadget id="calculator">(9/10) / (9/40)</gadget>
<output>4</output>

<result>4</result>