Master Li processes a batch of parts. If he makes 50 parts a day, it will be finished 8 days later than the original plan; if he makes 60 parts a day, he can finish it 5 days earlier. How many parts are there in this batch?
李师傅加工一批零件，如果每天做50个，要比原计划晚8天完成；如果每天做60个就可以提前5天完成．这批零件共有多少个？
<gadget id="calculator">8 + 5</gadget>
<output>13</output>

<gadget id="calculator">1 / 50</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">1 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/50) - (1/60)</gadget>
<output>1/300 = around 0.003333</output>

<gadget id="calculator">13 / (1/300)</gadget>
<output>3_900</output>

<result>3_900</result>