Posted by kheem on .
Cinema 2 has 25 seats in the first row and 30 rows in all. Each successive row contains one additional seat. How many seats are in the theater

math 
Reiny,
so you want
25+26+.. for 30 terms
an arithmetic series where a=25 , d=1 ,and n=30
sum(3) = (30/2)(50 + 29(1)) = 1185 
math 
Anonymous,
a1=25 d=1 n=30
sn=30/2{2(25)+(301)1}
sn=15(50+29)
sn=15(79)
sn=1,185 seats in the theatre 
math 
Denise,
a1=25 d=1 n=30
sn=30/2{2(25)+(301)1}
sn=15(50+29)
sn=15(79)
sn=1,185 seats in the theatre