There are two water inlet pipes A and B on a pool, the empty pool can be filled by opening the A pipe (1/2) hour alone, and the empty pool can be filled by opening the B pipe (1/5) hour, both pipes are opened at the same time , How many hours can the empty pool be filled? What is the correct column
一个水池上装有甲、乙两个进水管，单开甲管(1/2)小时可将空池注满，单开乙管(1/5)小时可将空池注满，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">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>