To fill a pool with water, pipes A and B are opened simultaneously for 3 hours, and 20% of the volume of the pool is filled. It is known that pipe A is opened alone for 20 hours to be filled, and pipe B is filled with 25 cubic meters per hour. What is the volume of this pool? (solution in various ways)
注满一池水，甲、乙两管同时开放3小时后，注入水池容积的20%．已知甲管单独开放20小时注满，乙管每小时注入25立方米，这个水池的容积是多少？(用多种方法解)
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">1 / 15</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">1 / (1/60)</gadget>
<output>60</output>

<gadget id="calculator">25 * 60</gadget>
<output>1_500</output>

<result>1_500</result>