project is done by one person alone, A takes 24 hours, B takes 20 hours, and C takes 30 hours. If A and C work together, how many hours can it be completed?
一项工程，由一人单独做，甲要24小时，乙要20小时，丙要30小时．如果甲、丙两人合做，多少小时可以完成？
<gadget id="calculator">1 / 24</gadget>
<output>1/24 = around 0.041667</output>

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

<gadget id="calculator">(1/24) + (1/30)</gadget>
<output>3/40 = around 0.075</output>

<gadget id="calculator">1 / (3/40)</gadget>
<output>40/3 = around 13.333333</output>

<result>40/3 = around 13.333333</result>