A pool can be filled with water in 10 hours by pipe A, and can be completely drained by pipe B in 15 hours. Now that pipes A and B are working at the same time, how many hours can the empty pool be filled with water?
一个水池用甲管往池内放水，10小时可以放满，用乙管从池内抽水，15小时可以把全池水抽完．现在甲乙两管同时工作，多少小时可以把空水池注满水？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/10) - (1/15)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / (1/30)</gadget>
<output>30</output>

<result>30</result>