A and B work together to process a batch of parts. The work efficiency ratio of A and B is 4:5. It is known that A processes 20 parts every day. After 8 days of joint processing, they just finish all the tasks (1/2) ． How many parts are there in this batch?
甲、乙两人共同加工一批零件，甲、乙的工作效率比是4：5，已知甲每天加工20个零件，两人共同加工了8天后正好完成了全部任务的(1/2)．这批零件共有多少个？
<gadget id="calculator">5 / 4</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">20 * (5/4)</gadget>
<output>25</output>

<gadget id="calculator">25 + 20</gadget>
<output>45</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">8 / (1/2)</gadget>
<output>16</output>

<gadget id="calculator">45 * 16</gadget>
<output>720</output>

<result>720</result>