A project can be completed in 12 days by teams A and B working together, and 20 days by team A alone. If Team B does it alone, how many days can it be completed?
一项工程，甲、乙两队合作12天完成，甲队单独做要20天完成．如果由乙队单独做，多少天可以完成．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">(1/12) - (1/20)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / (1/30)</gadget>
<output>30</output>

<result>30</result>