A swimming pool is equipped with a water inlet pipe and a drain pipe, and the water inlet pipe alone can fill the empty pool in 5 hours. Due to the negligence of the administrator, the two water pipes were opened at the same time, and it took 8 hours to fill the empty pool. How many hours will it take to drain the full pool if the drain is opened alone?
一个游泳池装有一个进水管和一个排水管，单开进水管5小时可将空池注满．由于管理员的疏忽，将两个水管同时打开，结果用了8小时才将空池注满．如果单独打开排水管，多少小时才能将满池水放完？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) * 8</gadget>
<output>8/5 = around 1.6</output>

<gadget id="calculator">(8/5) - 1</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">8 / (3/5)</gadget>
<output>40/3 = around 13.333333</output>

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