A project, three engineering teams A, B, and C alone will take 26, 39, and 52 days respectively. If the three engineering teams cooperate to complete it, how many days will it take?
一项工程，甲、乙、丙三个工程队单独完成，分别需26、39、52天，如果由三个工程队合作完成，则需多少天．
<gadget id="calculator">1 / 26</gadget>
<output>1/26 = around 0.038462</output>

<gadget id="calculator">1 / 39</gadget>
<output>1/39 = around 0.025641</output>

<gadget id="calculator">1 / 52</gadget>
<output>1/52 = around 0.019231</output>

<gadget id="calculator">(1/26) + (1/39) + (1/52)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / (1/12)</gadget>
<output>12</output>

<result>12</result>