A manuscript needs to be copied alone, A takes 15 hours, B takes 10 hours, and C takes 12 hours. Three people copy together. How many hours will it take to complete this manuscript?
一份稿件，单独抄，甲要15小时，乙要10小时，丙要12小时，三人合抄，完成这份稿件，需要多少小时？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</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) + (1/10) + (1/12)</gadget>
<output>1/4 = around 0.25</output>

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

<result>4</result>