For a project, if A and B work together, 1/2 of the project can be completed in 10 days; if C works alone, the project can be completed in 30 days; now A, B, and C work together, and it can be done in a few days Complete all projects?
一项工程，如果甲、乙合干，10天可以完成这项工程的(1/2)，如果丙单独干，30天完成这项工程，现在由甲、乙、丙合干，几天可以完成全部工程？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / 10</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/20) + (1/30)</gadget>
<output>1/12 = around 0.083333</output>

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

<result>12</result>