For a batch of parts, the time ratio required for A and B to complete alone is 3:5. Now the two are working together, and when the task is completed, A has processed 250 parts. How many parts are there in total?
一批零件，甲、乙两人单独完成所需的时间比是3：5．现两人合作，完成任务时，甲加工了250个，这批零件一共有多少个？
<gadget id="calculator">5 + 3</gadget>
<output>8</output>

<gadget id="calculator">5 / 8</gadget>
<output>5/8 = around 0.625</output>

<gadget id="calculator">250 / (5/8)</gadget>
<output>400</output>

<result>400</result>