Students clean the classroom, the students in group A can finish cleaning in 1/3 hour, and the students in group B can finish cleaning in 1/4 hour. How long does it take for two people to clean at the same time?
同学们打扫教室，甲组同学(1/3)小时可以打扫完，乙组同学(1/4)小时可以打扫完．两人同时打扫，需要多长时间才能打扫完？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / (1/3)</gadget>
<output>3</output>

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

<gadget id="calculator">1 / (1/4)</gadget>
<output>4</output>

<gadget id="calculator">3 + 4</gadget>
<output>7</output>

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

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