A job can be done by A alone every day (1/20), and B alone needs 12 days to complete this job. If two people cooperate to complete this job (8/15), how many days will it take?
一件工作，甲独做每天能完成这件工作的(1/20)，乙独做完成这件工作需要12天，如果两人合作完成这件工作的(8/15)，需要多少天？
<gadget id="calculator">8 / 15</gadget>
<output>8/15 = around 0.533333</output>

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

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

<gadget id="calculator">(1/20) + (1/12)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">(8/15) / (2/15)</gadget>
<output>4</output>

<result>4</result>