To process a batch of parts, lathe A can process 4 cases per day, and lathe B can process 5 cases per day. If two lathes work together, how many days will it take to process one case.
加工一批零件，用甲车床加工每天可以加工4箱，用乙车床加工每天可以加工5箱，两台车床合作，则加工1箱需要多少天．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<result>1/9 = around 0.111111</result>