To produce a batch of parts, worker A can complete it in 12 hours alone, and worker B can complete it in 15 hours alone. Worker A makes 20 more parts per hour than worker B. How many parts are there in this batch?
生产一批零件，甲工人独做12小时可以完成，乙工人独做15小时可以完成．甲工人每小时比乙工人多做20个零件，这批零件一共有多少个？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/12) - (1/15)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">20 / (1/60)</gadget>
<output>1_200</output>

<result>1_200</result>