A theater has 20 rows of seats. If there are 16 seats in the first row, 18 seats in the second row, 20 seats in the third row , and so on, how many seats are there in all?

Answer 1

This is an arithmetic series with a difference of 2

a₁ = 16

a₂₀ = 16 +19*2 = 54

The sum is 10(16 + 54) =700