To process a batch of parts, A first processed (1/5), and B processed (1/4). If 15 more parts are processed, half of this batch of parts is completed, how many parts are there in this batch?
加工一批零件，甲先加工了(1/5)，乙又加工了(1/4)，如果再加工15个正好完成这批零件的一半，这批零件有多少个？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

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

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

<gadget id="calculator">(1/2) - (1/5) - (1/4)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">15 / (1/20)</gadget>
<output>300</output>

<result>300</result>