It takes 20 hours for pipe A to fill a pool of water, and it takes 12 hours for pipe B to fill a pool of water. If two water pipes fill the pool at the same time, how many hours will it take to fill the pool?
甲水管注满一池水要20小时，乙水管注满一池水要12小时．如果两根水管同时向这个水池注水，多少小时可将这个水池注满？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/20) + (1/12)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">1 / (2/15)</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>