It takes 6 days for the apprentice to process a batch of parts alone, and the work efficiency of the master is twice that of the apprentice. In response to market demands, this batch of parts needs to be produced as soon as possible, so the unit requires the master and apprentice to work together at the same time. How many days can the task be completed?
加工一批零件，徒弟单独完成需要6天，师傅的工作效率是徒弟的2倍．应市场要求，需要尽快生产出这批零件，于是单位要求师徒两人同时合做，多少天能完成任务？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/6) * 2</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/6) + (1/3)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / (1/2)</gadget>
<output>2</output>

<result>2</result>