There are two water inlet pipes A and B in a pool, if A pipe is opened only, the pool can be filled in 20 minutes, and pipe B is opened only. It can be filled in 30 minutes. If both pipes are open for 5 minutes and pipe A is closed, how many minutes will it take to fill the pool?
一个水池有甲乙两个进水管，单开甲管，20分钟可以把水池注满，单开乙管．30分钟可以注满．如果两管齐开5分钟后关闭甲管，还要多少分钟才能把水池注满？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/20) + (1/30)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) * 5</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">1 - (5/12)</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">(7/12) / (1/30)</gadget>
<output>35/2 = around 17.5</output>

<result>35/2 = around 17.5</result>