For a batch of parts, it takes 10 days for Uncle Wang to make it alone, 12 days for Uncle Li to make it alone, and 15 days for Uncle Zhang to make it alone. In order to complete the task as soon as possible, how many days can they work together to complete half of all the parts?
有一批零件，王伯伯单独做要10天完成，李伯伯单独做要12天完成，张叔叔单独做要15天完成．为了尽快完成任务，他们一起做多少天可以完成全部零件的一半？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

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

<gadget id="calculator">(1/2) / (1/4)</gadget>
<output>2</output>

<result>2</result>