For a manuscript, A takes 3 hours to type, B takes 4 hours to type, and A and B jointly type in 1 hour to complete the manuscript.
一份稿件，甲用3小时打完，乙用4小时打完，甲乙合打1小时完成这份稿件的多少
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

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

<gadget id="calculator">(1/3) + (1/4)</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">(7/12) * 1</gadget>
<output>7/12 = around 0.583333</output>

<result>7/12 = around 0.583333</result>