batch of parts is divided into two days on average. The pass rate on the first day is 80%, and the pass rate on the second day is 90%. A total of 510 parts are passed in two days. How many parts are there in this batch?
一批零件平均分成两天做完，第一天的合格率是80%，第二天的合格率是90%，两天共合格了510个，这批零件共有多少个？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">(4/5) + (9/10)</gadget>
<output>17/10 = around 1.7</output>

<gadget id="calculator">(17/10) / 2</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">510 / (17/20)</gadget>
<output>600</output>

<result>600</result>