It takes 10 days for a batch of parts to be completed by master-student cooperation. It is known that it takes 15 days for the master to complete it alone. If the apprentice does it alone, how many days will it be completed?
一批零件，师徒合做要10天完成，已知师傅独做要15天完成，如果徒弟独做要多少天完成？
<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>1/30 = around 0.033333</output>

<gadget id="calculator">1 / (1/30)</gadget>
<output>30</output>

<result>30</result>