There is a pool, the empty pool can be filled with water in 10 hours if the water inlet pipe is opened alone, and the whole pool can be filled with water in 15 hours if the water outlet pipe is opened alone.
有一水池，单开进水管10小时可将空池放满水，单开出水管，15小时可将整池水放完，现在两管齐开，几小时可将空池注满水？
<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>