A swimming pool has three water pipes A, B, and C. If pipe A is opened alone, it takes 20 hours to fill the pool; when pipes A and B are opened together, it takes 12 hours to fill the pool; when pipes B and C are opened together, it takes 10 hours to fill the pool. So, how many hours does it take to fill the pool with a single open pipe?
游泳池有甲、乙、丙三个注水管．如果单开甲管需要20小时注满水池；甲、乙两管合开需要12小时注满水池；乙、丙两管合开需要10小时注满水池．那么，单开丙管需要多少小时注满水池？
<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 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/12) - (1/20)</gadget>
<output>1/30 = around 0.033333</output>

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

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

<gadget id="calculator">(1/10) - (1/30)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / (1/15)</gadget>
<output>15</output>

<result>15</result>