The two masters and apprentices planned to process 50 parts. In the first half of the month, the master processed 20 parts and the apprentice processed (1/5) of the plan. How much of the plan is left unprocessed?
师徒两人计划加工50个零件，上半月师傅加工了20个，徒弟加工了计划的(1/5)．还剩计划的几分之几没有加工？
<gadget id="calculator">20 / 50</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (2/5) - (1/5)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>