To make a batch of parts, the apprentice first does it alone for 4 days, and then cooperates with the master for 8 days, thus completing (4/5) of the total number of parts. It is known that the ratio of work efficiency between master and apprentice is 3:2. If two masters and apprentices work together on this batch of parts at the same time, how many days will it take to complete.
做一批零件，徒弟先独做4天，然后与师傅合做8天，这样完成了零件总数的(4/5)．已知师徒工作效率的比是3：2．如果这批零件师徒两人同时合做，需要多少天完成．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">12 * (2/3)</gadget>
<output>8</output>

<gadget id="calculator">8 + 8</gadget>
<output>16</output>

<gadget id="calculator">(4/5) / 16</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) * (2/3)</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">1 / (1/12)</gadget>
<output>12</output>

<result>12</result>