To process a batch of parts, A alone can complete it in 12 hours, and B alone can complete it in 18 hours. If A works alone for 2 hours and then the two work together, the task can be completed in a few hours.
加工一批零件，甲单独做12h完成，乙单独做18h完成，若甲先独做2h后两人合做，合做几小时可以完成这项任务．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) * 2</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 - (1/6)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">(1/12) + (1/18)</gadget>
<output>5/36 = around 0.138889</output>

<gadget id="calculator">(5/6) / (5/36)</gadget>
<output>6</output>

<result>6</result>