后来补充的句子中：第二个是对的，其它两个有点令人费解。 月和月份在你的例句 “1. 我10月要参加一个本科入学考试。3. 我10月份要参加一个本科入学考试。”中，意思是一样的。

没有对错，但他们的意思都是不一样的。几月指的是公历，几月份指的是农历。1和3有可能在一个月里，但肯定不是同一天。2是很明显的10月之后。

i'll say the same as all above. 1 and 3 is exactly the same. but the 2 is abit different, means after the Oct............. (which is surely not in oct' but could be november, december or even january..........etc) and when you put (個） it make the sentence weird, and the 1 and 3 is meaningless(it is not the way we speak it )　. but, this time, the 2 one is correct alone.

I am about to take an exam in October.我将在十月份参加一个考试。 I am about to take an exam after October 我将在十月份以后参加一个考试。 “10个月” mean the time of ten months I am about to take an exam after ten months. 我十个月后要参加一个考试 。 “in ten months" means 在将来的10个月以内 not more than that The work must be finished in the next ten months .这项工作必须在未来的十个月内完成。

the third is the same meaning as the first; the second sentence is not a good expression ,because it puzzled the listener. it can means 1、I will have an exam after oct.- 我十月份后要参加一个考试。 2、I will have an exam in ten months' time. 我十个月后要参加一个考试。 now ,the difference between "月" and "月份" you can use “月" instead of "月份" in any case. if your say do sth in which month, you can use 月份 instead of 月,otherwise,you can't. especially means "how long of the time", for example right:我需要5个月的时间复习。 wrong:我需要5个月份的时间复习。