"A week is seven days."
Translation:Bir hafta yedi gündür.
"-Dür" is actually "-dir". We are using this to tell certain informations like "Hava bir gazdır, üçgenin iç açıları toplamı 180 derecedir..." Or you can use it when you are talking about possibility Maybe I don't like him? Belki ben onu sevmiyorumdur/hoşlanmıyorumdur? I hope I could help.
For me, "Bir hafta, yedi gün" is completely fine. With a comma in between and a half a second pause when speaking. I can easily imagine a boss saying: "Bir hafta, yedi gün, arkadaşlar, hepiniz biliyorsunuz, ona göre yetiştirin işleri… bla bla bla". It's completely natural to me in the spoken language. But Selcen insists that it sounds bad, and I understand that point of view also, but only if I were to see it in a book. When speaking, who cares, I wouldn't use it. This is one of those things where natives' opinions divide.
When you use a digit with a noun, you should NEVER use the plural suffix on the end of the noun. This is redundant and grammatically incorrect in Turkish. That means you should say “iki kedi” and not “iki kediler.”
'The above statement is extracted from Tips and Notes of Numbers lesson'