Process a batch of parts, the master completes it in 8 hours, and the apprentice completes it in 10 hours. The master and apprentice worked together for 4 hours, and a total of 270 parts were processed. How many parts are in this batch?
加工一批零件，师傅8小时完成，徒弟10小时完成．师徒合做4小时，共加工了270个，这批零件多少个？
<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/8) + (1/10)</gadget>
<output>9/40 = around 0.225</output>

<gadget id="calculator">(9/40) * 4</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">270 / (9/10)</gadget>
<output>300</output>

<result>300</result>