У тижні сім днів.

There are seven days in a week.

Breakdown of У тижні сім днів.

• у: in
• день: the day
• тиждень: the week
• сім: seven

Questions & Answers about У тижні сім днів.

Why is тиждень changed to тижні here?

Because у meaning in normally requires the locative case.

• Dictionary form: тиждень = week
• Locative singular: у тижні = in a week / in the week

So тижні is not a plural here. It is a singular locative form.

Why is it сім днів, not сім дні?

After numerals 5 and higher, Ukrainian nouns usually take the genitive plural.

So:

• один день
• два / три / чотири дні
• п’ять / шість / сім днів

That is why the sentence has сім днів.

Why is there no word for are in the sentence?

In Ukrainian, the present-tense verb to be is often omitted in simple statements.

So Ukrainian can say:

• У тижні сім днів.

where English needs something like:

• There are seven days in a week.

You can also say У тижні є сім днів, with є, but it is not required.