If there are 2040 seats in a section of a stadium, 20 seats in the first row, and 4 more seats in each row, how many rows are there?

2040 = n/2 (20 + (n-1) 4)

4080 = n (20+4n-4)

4080 = 20n + 4n^2 - 4n

1020 = 4n + n^2

n^2 + 4n - 1020 = 0

use common formula (can't write out so just look at answers. sorry)

which gives answers of n=-34 and n=30. since n can only be positive, n=30 so there are 30 rows. I liked that challenge

Nth term: 16+4n

2040=16+4n

Subtract 16 from both sides

2024=4n

Divide by 4

506=n

506 rows