A project can be completed by team A alone in 20 days and by team B in 30 days. Now, Team A will work for one day, then Team B will take over from Team A for one day, and on the third day, Team A will take over from Team B for another day..., so alternately, when Team B finishes its work, how many days will it take to complete the task?
一项工程，甲队独做需要20天完成，乙队独做需要30天完成．现在由甲队施工一天，然后由乙队接替甲队施工一天，第三天再由甲队接替乙队施工一天…，如此交替，最后乙队结束工作，多少天完成任务？
<gadget id="calculator">12 + 12</gadget>
<output>24</output>

<result>24</result>