A pool is equipped with two water inlet pipes A and B. Open pipe A (1/2) hour to fill the empty pool, and pipe B (1/5) hour to fill the empty pool. Open both pipes at the same time. Hours can fill an empty pool? What is the correct column
一个水池装有甲、乙两个进水管，单开甲管(1/2)小时将空池注满，单开乙管(1/5)小时将空池注满，两管同时打开，几小时可以注满空池？正确列式是多少
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<result>1/7 = around 0.142857</result>