pool is equipped with 3 water pipes, the pool can be filled in 20 minutes by opening pipe A alone, the pool can be filled in 30 minutes by opening pipe B alone, and the full pool can be filled by opening pipe C in 60 minutes. Now the three water pipes can be filled at the same time Open, how many minutes does it take to fill the pool?
一个水池装有3个水管，单开甲管20分钟可将水池放满，单开乙管30分钟可将水池放满，单开丙管60分钟可将满池水放完，现在三个水管同时打开，经过多少分钟可将水池放满？
<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 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/30) - (1/60)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/20) + (1/60)</gadget>
<output>1/15 = around 0.066667</output>

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

<result>15</result>