A piece of land can be sown by tractor A in 6 hours, and can be sown by tractor B in 4 hours. If two tractors sow seeds at the same time, how many hours can they be sown?
一块地，用甲拖拉机播种，6h可播完，用乙拖拉机播种，4h可播完，如果两台拖拉机同时播种，几小时可以播完？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/6) + (1/4)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">1 / (5/12)</gadget>
<output>12/5 = around 2.4</output>

<result>12/5 = around 2.4</result>