A pool has two water inlet pipes, A and B, and the ratio of the water output of the two pipes in one minute is 4:5. Open pipe A alone for 20 minutes to fill the empty pool. If pipe B is opened alone, how many minutes will it take to fill the empty pool?
一个水池有甲乙两个进水管，甲乙两管一分钟出水量的比是4：5．单独打开甲管20分钟可以把空池注满，如果单独打开乙管，需要多少分钟能把空池注满．
<gadget id="calculator">5 / 4</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">20 / (5/4)</gadget>
<output>16</output>

<result>16</result>