A batch of parts can be completed by A alone in 6 hours, B by himself in 9 hours, and the number of parts that can be completed by two people in 2 hours.
一批零件，甲独做6小时完成，乙独做9小时完成，两人合做2小时完成这批零件的多少．
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

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

<gadget id="calculator">(1/6) + (1/9)</gadget>
<output>5/18 = around 0.277778</output>

<gadget id="calculator">(5/18) * 2</gadget>
<output>5/9 = around 0.555556</output>

<result>5/9 = around 0.555556</result>