reservoir has two water inlet pipes A and B. If pipe A is opened alone, it takes 12 hours to fill up, and pipe B alone takes 18 hours to fill up. Now, if both pipes A and B are opened at the same time, how many hours will it take Fill the pool.
一蓄水池有甲、乙两个进水管，如果单独开甲管需12个小时注满，单独开乙管需18小时注满，现在同时打开甲、乙两个进水管，需要多少个小时注满水池．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">(1/12) + (1/18)</gadget>
<output>5/36 = around 0.138889</output>

<gadget id="calculator">1 / (5/36)</gadget>
<output>36/5 = around 7.2</output>

<result>36/5 = around 7.2</result>