There are three water injection pipes A, B, and C in the swimming pool. It takes 20 hours to open pipe A to fill the pool, open pipes A and B together for 8 hours, and pipes B and C to fill water in 6 hours. Then open pipe C alone How many hours does it take to fill the tube?
游泳池有甲、乙、丙三个注水管，单开甲管20小时注满水池，甲、乙两管合开8小时注满，乙、丙两管合开6小时注满，那么单开丙管需几小时注满？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/8) - (1/20)</gadget>
<output>3/40 = around 0.075</output>

<gadget id="calculator">(1/6) - (3/40)</gadget>
<output>11/120 = around 0.091667</output>

<gadget id="calculator">1 / (11/120)</gadget>
<output>120/11 = around 10.909091</output>

<result>120/11 = around 10.909091</result>