Question

A large multiplex movie house has many theaters. The largest theatre has 36 rows. There are 20 seats in the first row. Each row has four seats more than the previous row. How many total seats are there in this theatre?

Answer 1

2880 seats

Explanation:

r1 r2 r3 r36

20 + 20+4 + 20+4+4 + ···+20+4×35

total seats = ((20 + 20+4×35)÷2)×36= 2880