The master and the apprentice complete a task, the master completes it in 20 days, and the apprentice can complete one-third of the task in 10 days. How many days will it take for the master-student to do two-thirds of this task?
师徒两人完成一项任务，师傅20天完成，徒弟10天能完成这项任务的三分之一．师徒合做这项任务的三分之二需要几天？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

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

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/3) / 10</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">(2/3) / (1/12)</gadget>
<output>8</output>

<result>8</result>