A project is done alone. A needs 10 days to complete, and B needs to finish in 15 days. At the beginning, the two work together. Because of the work, A needs to be transferred in the middle. As a result, B and the other took 9 days to complete, and A was transferred in the middle of the day. of?
一项工程，单独做，甲要10天完成，乙要15天完成，开始二人一起干，因工作需要甲中途调走，结果乙一共用了9天完成，甲中途是在第几天调走的？
<result>5</result>