How to write an equation

Question

A theater is divided in 2 sections A&B. Each section has 10 rows. The first row has 20 seats and each row after that has 2 more seats. Find total number of seats

Answer 1

There is a way to do this with function notation, but I would just jump right in and list out the seats with one of the sections:

10 / 12 /14/ 16 / 18 / 20 / 22 / 24 / 26 /28

The shortcut to adding these numbers (without a calculator) is to add the first and last number (10 + 28). That's 38. After that add the next two in (12 + 26), which again is 38. So how many pairs of 38? 5

38 x 5 = 190 seats in section A

Double it for section B and the theater has 380 seats for people to watch the Nickelback concert.