Answer:
The number of days is 13.
Explanation:
It is given that a birds watcher saw 3 blue jays on the first day of his vacation. Each day after that he saw 2 more blue jays than he did on the previous day.


...
It means the series is
3,5,7,..., 27
The first term of series is 3 and the common differences is 2.
The formula of nth term is

Substitute
, a=3 and d=2.





Therefore the number of days is 13.