It takes 15 hours for A and B to complete a job, 12 hours for B and C to do it together, and 10 hours for A and C to do it together. How many hours will it take for A, B, and C to work together?
完成一件工作，甲、乙两人一起做需15小时，乙、丙两人一起做需12小时，甲、丙两人一起做需10小时．甲、乙、丙三人一起做需几小时才能完成？
<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</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/4) / 2</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">1 / (1/8)</gadget>
<output>8</output>

<result>8</result>