A, B, C, and D cooperate to process a batch of parts, A processes 50% of the other three's processing, B's processing is the remaining three's (1/3), and C's processing is the remaining three's 20% of the processing, Ding processed 30 parts. How many parts are there in this batch?
甲、乙、丙、丁四人合作加工了一批零件，甲加工的是其余三人加工的50%，乙加工的是其余三人加工的(1/3)，丙加工的是其余三人加工的20%，丁加工了30个零件．这批零件共有多少个？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

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

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 - (1/3) - (1/4) - (1/6)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">30 / (1/4)</gadget>
<output>120</output>

<result>120</result>