about...

[navi tasan]

Are these sentences correct:
1-He is a writer about whom I don't know how many books he has written.
2-He is a writer who has written I know not how many books.
3-He is a writer who has written I don't know how many books.

4-He was the writer that I didn't know had signed the petition.
5-He was the writer about whom I didn't know that he had signed the petition.

 

[Tdol]

Are these sentences correct:
1-He is a writer about whom I don't know how many books he has written.
2-He is a writer who has written I know not how many books.
3-He is a writer who has written I don't know how many books.

4-He was the writer that I didn't know had signed the petition.
5-He was the writer about whom I didn't know that he had signed the petition.

I'd say number 1 is incorrect- 'about doesn't go with know when it's a figure.

Number 5 is tarred with the same brush, IMO. I'm not as sure that I could call it incorrect, but I would advise against it. ;-)