To process a batch of parts, the master processed 1200 pieces, accounting for 2/5 of the total number of parts, and the rest were distributed to the master and apprentice according to the ratio of 5:4. How many pieces did the apprentice process when the task was completed?
加工一批零件，师傅加工了1200个，正好占零件总数的(2/5)，余下的按照5：4的比例分配给师徒二人加工，完成任务时徒弟加工了多少个？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1_200 / (2/5)</gadget>
<output>3_000</output>

<gadget id="calculator">3_000 - 1_200</gadget>
<output>1_800</output>

<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">1_800 * (4/9)</gadget>
<output>800</output>

<result>800</result>