Salget varer en uke.

Because salget is the definite form, meaning the sale.

• salg = sale
• salget = the sale

In Norwegian, the definite article is usually added to the end of the noun rather than written as a separate word in front:

• en bil = a car
• bilen = the car

Here, salg is a neuter noun, so the definite ending is -et:

• et salg = a sale
• salget = the sale

Varer is the present tense of the verb å vare, which means to last.

So:

• å vare = to last
• varer = lasts / is on for

Examples:

• Møtet varer en time. = The meeting lasts an hour.
• Ferien varer to uker. = The vacation lasts two weeks.

In your sentence:

• Salget varer en uke. = The sale lasts a week.

Yes, it looks the same in writing, and that can be confusing.

There are two different things here:

1. å vare = to last

   • varer = lasts

2. en vare = a product / an item / a good

   • varer = goods / products

So varer can mean either:

• lasts (verb)
• goods (plural noun)

In Salget varer en uke, it is clearly the verb, because salget is the subject and en uke tells you the duration.

Because Norwegian, like English, can often use a direct time expression after verbs of duration.

Compare English:

• The sale lasts a week.

You do not say:

• The sale lasts for a week is possible in English, but a week without for is also completely natural.

Norwegian works similarly:

• Salget varer en uke.

The phrase en uke is simply expressing duration: how long something lasts.

More examples:

• Filmen varer to timer. = The film lasts two hours.
• Kurset varer tre dager. = The course lasts three days.

Good question. Uke is traditionally a feminine noun, so you may see:

• ei uke = a week

However, in Bokmål, many feminine nouns can also be treated as common gender, so en uke is also correct and very common.

So all of these can occur in Bokmål:

• en uke
• ei uke

And in the definite form:

• uken
• uka

This means the sentence could also appear as:

• Salget varer ei uke.

That is also correct.

The sentence has standard Norwegian main clause word order:

Subject + Verb + Time expression

• Salget = subject
• varer = verb
• en uke = duration/time expression

So:

• Salget varer en uke.

This is very similar to English:

• The sale lasts a week.

Nothing unusual is happening with the word order here.

Sometimes learners want to add i, but with å vare, the most natural pattern is usually just the duration directly:

• Salget varer en uke.

Using i en uke is generally less natural in this kind of sentence if you simply mean total duration.

A useful rule of thumb:

• after å vare, use the length of time directly:
  • varer en dag
  • varer to måneder
  • varer lenge

So the best version here is:

• Salget varer en uke.

You would change the time expression:

• Salget varer to uker. = The sale lasts two weeks.
• Salget varer tre uker. = The sale lasts three weeks.

Notice:

• en uke = singular
• to uker = plural

After numbers greater than one, Norwegian normally uses the plural noun:

• to dager
• tre måneder
• fire år

Yes. Salg can refer to:

• a sale in the sense of a sales event, discount sale, promotion
• sale/selling in a more general business sense

The exact meaning depends on context.

For example:

• Salget varer en uke. = clearly the sale as an event
• Salg av biler er vanskelig nå. = The selling of cars is difficult now

So in your sentence, context tells us it means a sales event.

In careful speech, salget is roughly pronounced like SAHL-get, but the exact sound can vary by dialect and speed.

A few helpful points:

• salg ends with lg, which can be a little tricky for English speakers
• in salget, the ending -et is added to salg
• the g is not strongly exploded the way an English speaker might expect

You do not need to exaggerate every consonant. The most important thing is to keep the stress on the first syllable:

• SAL-get
• VA-rer
• en U-ke

Yes, but the meaning changes slightly.

• Salget varer en uke. = states the duration as a fact
• Salget skal vare en uke. = The sale is supposed to last a week / is planned to last a week

So:

• varer = simple statement of fact
• skal vare = plan, intention, or expectation

If you are just describing the sale, Salget varer en uke is the straightforward choice.