Translation:The car is on the fifth avenue.
I am almost certain that I have not come across "πέμπτη" = fifth before this in the Duo lessons. It does make an appearance in Dates and Time as "Thursday" with a capital Π. And for that matter "δεύτερος" = second is still missing. Now I have become aware of the connection with days of the week I see that Monday is there as Δευτέρα.
δευτέρα is in fact the old feminine form of the adjective.
Modern Greek uses δεύτερη (it doesn't change the eta to alpha after rhos any more, nor does the position of the accent change on adjectives), but the name of the day of the week fossilised the old form.