For a batch of parts, 1/3 of the total number is processed on the first day, and 20% of the total number is processed on the second day, and there are still 210 parts that have not been processed. How many parts are there in total?
一批零件，第一天加工了总数的(1/3)，第二天加工了总数的20%，这时还剩210零件没有加工．这批零件一共有多少个？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/3) - (1/5)</gadget>
<output>7/15 = around 0.466667</output>

<gadget id="calculator">210 / (7/15)</gadget>
<output>450</output>

<result>450</result>