Mellan tolv och fjorton timmar varje dag (vuxna).
Is it correct to say "Hur länge sover hundar i genomsnitt?"?
You could say that, but it would not correspond to much but rather long.
Is länge for time while långt is for distance or some other measure or space?
As a native English speaker (and writer, as an attorney), I placed "on average" before "do dogs sleep" because it sounds and looks better to me. I think either way ought to be fine in the translation.
Kan man också använda "i allmänhet" istället "i genomsnitt"? Eller har det då en annan mening?
How much does the average dog sleep was marked wrong
Yes, the average is referring to the sleep and not to the dog.
How much on average do dogs sleep? was marked wrong. I do not see why at all.
Kan någon som har en hund svara det här frågan?