One water inlet pipe and three same drain pipes are installed in a pool, and the pool can be filled with water in 20 minutes if the water inlet pipe is opened alone; if only one drain pipe is opened, the water in the pool can be completely drained in 45 minutes, now there are (2/3) For pool water, if the four pipes are opened at the same time, how long will it take to drain the water?
一个水池装了一根进水管和三根同样的排水管，单开进水管20分钟可注满水水池；单开一根排水管，45分钟可将满池水排完，现在有(2/3)池水，如果四管同时打开，多少分钟将水排完？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 / 45</gadget>
<output>1/45 = around 0.022222</output>

<gadget id="calculator">(1/45) * 3</gadget>
<output>1/15 = around 0.066667</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>