7.8 Having and Being in the Past

In 7.8, there is the following sentence:

Wir waren sehr beschäftigt in den letzten Wochen.
We were very busy in the last (few) weeks.

May I ask why it would not be "die letzten Wochen" since "Wochen" is plural?

Thank you,
Grace

Den is the dative plural  form of der, it is dative because it follows in which requires the dative in this instance.
I don't have level 1 so I don't know if this has been covered yet in the course. If it hasn't been covered, it might be best remember ​in den letzten Wochen as a stock phrase or "chunk" - "in the last (few) weeks"

Hi SooK and sfpugh, 

sfpugh is right, the "in" in your sentence above is a temporal preposition which requires the dative case. It gives the answer to the question word wann when asking:

"Wann waren wir sehr beschäftigt?" - "When were we very busy?"
"In den letzten Wochen." - "In the last (few) weeks."

You can learn more about the dative case in lesson 9.11 A Case in Point - Dative and 14.7 German Cases – Part 2.

Viele Grüße
Julia