Answer:
A. 1130
Step-by-step explanation:
find [tex]a_{20}[/tex] first:
[tex]a_{n} =a_{1}+(n-1)d\\a_{20}=9+(20-1)5\\a_{20}=9+(19)5\\a_{20}=9+95\\a_{20}=104[/tex]
Solution:
[tex]S_{n}= \frac{n}{2} (a_{1}+a_{n})\\S_{n}= \frac{20}{2} (9+104)\\S_{n}= \frac{20}{2} (113)\\S_{n}= 10(113)\\S_{n}= 1130[/tex]
