project can be completed by team A alone in 20 days, and by team B in 30 days. If the two teams work together, how many days can the whole process be completed (3/4).
一项工程，单独做甲队要20天完成，乙队要30天完成，两队合做，多少天可以完成全程的(3/4)．
<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>