A theater has 35 rows of chairs. The first row has 20 chairs, the second has 22, the third has 24, and so on. In total, the theater seats _____ people.
Here we have an arithmetic sequence: a 1 = 20, d = 2, n = 35 S n = n/2 ( a 1 + a n ) a 35 = a 1 + 34 d = 20 + 34 2 = 20 + 68 = 88 S 35 = 35/2 ( 20 + 88 ) = 35 / 2 108 = 1,890 Answer: In total, the theater seats 1,890 people
