To produce a batch of parts, A alone takes 10 days to complete, B alone takes 15 days to complete, and C alone takes 12 days to complete. If three people work together, how many days can it be completed?
生产一批零件，甲单独做需要10天完成，乙单独做需要15天完成，丙单独做需要12天完成．如果三人合作，多少天可以完成？
<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 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/10) + (1/15) + (1/12)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / (1/4)</gadget>
<output>4</output>

<result>4</result>