A project can be completed in 3 hours and B in 4 hours. Now let A do it for 2 hours first, and how many hours will it take for the remaining tasks to be completed by the two of them.
一项工程，甲用3小时可完成，乙用4小时可完成．现在先由甲做2小时，余下的任务两人合作完成，又用了多少小时．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/3) * 2</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</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">(1/3) / (7/12)</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>