If A alone takes 7 hours to complete a job and B alone takes 12 hours to complete the job, when two people work together to complete the job, how much more will A do than B?
一件工作甲独做要7小时完成，乙独做要12小时完成，二人合做完成这项工作时，甲比乙多做这项工作的多少．
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/7) + (1/12)</gadget>
<output>19/84 = around 0.22619</output>

<gadget id="calculator">1 / (19/84)</gadget>
<output>84/19 = around 4.421053</output>

<gadget id="calculator">(1/7) - (1/12)</gadget>
<output>5/84 = around 0.059524</output>

<gadget id="calculator">(84/19) * (5/84)</gadget>
<output>5/19 = around 0.263158</output>

<result>5/19 = around 0.263158</result>