Two water pipes in A and B are separately opened, and it takes 20 hours and 16 hours to fill a pool of water respectively. Pipe C is opened separately, and it takes 10 hours to drain a pool of water. If there is no water in the pool, both pipes A and B are opened at the same time. After 5 hours, drain pipe C is opened again. How many hours will it take for the pool to fill up?
甲乙两个水管单独开，注满一池水，分别需要20小时，16小时．丙水管单独开，排一池水要10小时，若水池没水，同时打开甲乙两水管，5小时后，再打开排水管丙，水池注满还要多少小时．
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 16</gadget>
<output>1/16 = around 0.0625</output>

<gadget id="calculator">(1/20) + (1/16)</gadget>
<output>9/80 = around 0.1125</output>

<gadget id="calculator">(9/80) * 5</gadget>
<output>9/16 = around 0.5625</output>

<gadget id="calculator">1 - (9/16)</gadget>
<output>7/16 = around 0.4375</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/16) - (1/10)</gadget>
<output>-3/80 = around -0.0375</output>

<gadget id="calculator">(1/20) + (-3/80)</gadget>
<output>1/80 = around 0.0125</output>

<gadget id="calculator">(7/16) / (1/80)</gadget>
<output>35</output>

<result>35</result>