What is correct?
Did you sleep well? or Did you slept well?
Thank you in advance

Question

What is correct?
Did you sleep well?  or Did you slept well? 
Thank you in advance

Answer

Did you sleep well ? is the correct thing to say. (Simple past)

Have you slept well ? is another way of using slept. (Present perfect)

though they might be used in different contexts. Read more about these tenses to have a better understanding. The difference take s little bit of effort to understand.
http://www.ego4u.com/en/cram-up/grammar/simpas-preper

Answer

Did you sleep well! Or did you sleep well last night

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