There are two piles of coal A and B with the same amount of coal. If only one pile of coal is shipped, then it takes 20 hours for car A, 24 hours for car B, and 30 hours for car C. Now car A is loading pile A of coal, car B is loading coal pile B, and car C is starting to load pile A of coal, and then turns to pile coal B in the middle. The three cars start at the same time and finish loading the two piles of coal at the same time. How long did it take for truck C to load pile A of coal?
有A，B两堆同样多的煤，如果只装运一堆煤，那么甲车需要20时，乙车需要24时，丙车需要30时．现在甲车装运A堆煤，乙车装运B堆煤，丙车开始先装运A堆煤，中途转向装运B堆煤，三车同时开始，同时结束装完这两堆煤．丙车装运A堆煤用了多少时间？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<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">(1/20) + (1/24) + (1/30)</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">2 / (1/8)</gadget>
<output>16</output>

<gadget id="calculator">(1/20) * 16</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / (1/30)</gadget>
<output>6</output>

<result>6</result>