The master and apprentice processed a batch of parts. After 4 hours, the master completed (1/4) of this batch of parts, and the apprentice completed 12.5% of this batch of parts, and there were still 20 less parts. The master and apprentice continued to process for 8 hours and just finished. How many parts are there in this batch?
师徒共加工一批零件，4小时后，师傅完成这批零件的(1/4)，徒弟完成这批零件的12.5%还少20个，师徒继续加工8小时正好完成．这批零件共有多少个？
<gadget id="calculator">4 + 8</gadget>
<output>12</output>

<gadget id="calculator">12 / 4</gadget>
<output>3</output>

<gadget id="calculator">3 * 20</gadget>
<output>60</output>

<gadget id="calculator">12.5 / 100</gadget>
<output>0.125</output>

<gadget id="calculator">3 * 0.125</gadget>
<output>0.375</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) * 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/4) - (1/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">0.375 - (1/4)</gadget>
<output>0.125</output>

<gadget id="calculator">60 / 0.125</gadget>
<output>480</output>

<result>480</result>