"They are coming in fifteen minutes."
Translation:De kommer om en kvart.
’For fifteen minutes’ equals i en kvart in Swedish, and ’in fifteen minutes’ equals om en kvart. Swedish uses different prepositions than English does in this case.
"på en kvart" means that it takes 15 minutes to do something, "om en kvart" means that something will happen in 15 minutes time.
I'm not sure that's correct. My understanding is that "i en kvart" means that it takes 15 minutes to do something.
I think that "i en kvart" is how long you have been doing something:
Jag har väntat i en timme - I have been waiting for an hour
Jag kan köra till Stockholm på en timme - I can drive to Stockholm in an hour
Filmen börjar om en timme - the film starts in an hour
Jenny and Jean, your comments are helpful. But can't "i" also be used when talking about the future? For example, "I will wait for 15 minutes". Wouldn't the Swedish translation of that sentence use "i"?