To complete some parts, A can complete it in (1/6) days alone, and B can complete it in (1/9) days alone. How many days can A and B cooperate to complete these parts.
完成一些零件，甲独做(1/6)天完成，乙独做(1/9)天完成．甲乙合作多少天能完成这些零件．
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / (1/6)</gadget>
<output>6</output>

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

<gadget id="calculator">1 / (1/9)</gadget>
<output>9</output>

<gadget id="calculator">6 + 9</gadget>
<output>15</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<result>1/15 = around 0.066667</result>