A project can be completed in 20 days by A alone, and 30 days by B alone. If A and B cooperate to complete (3/4) of the whole project, how many days will it take?
一项工程，甲独做要20天完成，乙独做要30天完成，如果甲乙合作完成全工程的(3/4)，需多少天．
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/20) + (1/30)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(3/4) / (1/12)</gadget>
<output>9</output>

<result>9</result>