Processing the same batch of parts, it takes 10 days for the master to process alone, and 15 days for the apprentice to process alone. Now the master and apprentice work together, how many days will it take to complete?
加工同一批零件，师傅单独加工需要10天完成，徒弟单独加工需要15天完成．现在师徒二人共同加工，需要多少天完成？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/10) + (1/15)</gadget>
<output>1/6 = around 0.166667</output>

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

<result>6</result>