1. I didn't knwon anyone in my room.

2. I knew no one in my room.
3. I knew nobody in my room.
4. I didn't know all the students in my room.
5. I didn't know all the classmates in my room.
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If "I" is a student, do all the sentences mean the same?

3 answers

I don't want to guess for you but I'm assuming that they should all make sense and mean the same? Maybe u can try substituting "I" for a name like John or something and then see if the sentences make sense? Hope this helps :)
1. I didn't know anyone in my room.
2. I knew no one in my room.
3. I knew nobody in my room.
4. I didn't know all the students in my room.
5. I didn't know all the classmates in my room.
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All sentences are grammatical. #1,2,and 3 are the same. #4 and #5 are different from the other sentences. I knew some of the students in the room. I didn't know the other students in the room.
All your sentences in the second set are correct. And, yes, the meaning shifted a bit in the last two. =)