Question

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.

Answer 1

Arithmetic sequence?

Answer 2

\[\sum_{i=0 \to 34}20+2{i}\]

Answer 3

The sum of the first n terms of an arithmetic sequence is
n/2[a1+an], where an=a1+(n-1)d, where d is the common difference, which
is 2 in our case. Also n=35 and a35=20+34(2)=88, so S_35=
35/2[20+88]=1890