Posted by **kheem** on Thursday, March 7, 2013 at 8:02am.

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**, Thursday, March 7, 2013 at 10:27am
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**, Friday, July 8, 2016 at 5:33am
a1=25 d=1 n=30

sn=30/2{2(25)+(30-1)1}

sn=15(50+29)

sn=15(79)

sn=1,185 seats in the theatre

- math -
**Denise**, Friday, July 8, 2016 at 5:34am
a1=25 d=1 n=30

sn=30/2{2(25)+(30-1)1}

sn=15(50+29)

sn=15(79)

sn=1,185 seats in the theatre

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