It takes 12 hours for A and B to do a job together, 12 hours for B and C to do it together, 10 hours for A and C to do it together, and how many hours for A, B, and C to do it together? Finish?
完成一件工作，甲、乙两人一起做需要12小时，乙、丙两人一起做需要12小时，甲、丙两人一起做需要10小时，甲、乙、丙三人一起需要几小时才能完成？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">(1/12) + (1/12) + (1/10)</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">(4/15) / 2</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">1 / (2/15)</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>