pool is equipped with a water inlet pipe and a drain pipe. Open the water inlet pipe for 15 minutes to fill the empty pool, and open the drain pipe for 20 minutes to drain the full water. First open the water pipe for 5 minutes, and then open both pipes together , how many minutes later can the pool be filled?
一个水池安装有一个进水管和一个排水管，单开进水管15分可以把空池注满，单开排水管20分可把满池水放完，先开进水管5分，再两管齐开，再过多少分可以注满水池？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 5</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

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

<gadget id="calculator">(1/15) - (1/20)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(2/3) / (1/60)</gadget>
<output>40</output>

<result>40</result>