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I tried to search this question in your archives but I was always redirected to "the difference between be used to + N and used to + V". And I can't find your FAQ tab.

Anyway, my question is what is the Y/N question form of the sentence "S + used to + V" (e.g. I used to work there.)

Is it "Did you use to work there?"
or "Did you used to work there?"

I saw a book before that says they're both OK. Now a native speaker in my school says only the latter is correct. Google results also affirm the native speaker's opinion.
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They are both 'OK'. Swan says the former is common and the latter, an alternative, is considered incorrect by 'many'.
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 Mister Micawber's reply was promoted to an answer.
Mr WordyHere are two previous threads on this topic:
http://www.EnglishForward.com/English/DidYouUsedToDidYouUseTo/kclml/post.htm
http://www.EnglishForward.com/English/DidYouUsedToDidYouUseTo/2/kclml/Post.htm

Sorry, make that one thread spread over two pages.
Mister MicawberSwan says the former is common and the latter, an alternative, is considered incorrect by 'many'.
It's strange because the former, to me, looks like a combination of words that could not possibly be grammatical. I have never understood this construction.
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