Answer: there are 580 seats
Explanation:
The number of seats in each row is increasing in arithmetic progression.
The formula for determining the sum of n terms of an arithmetic sequence is expressed as
Sn = n/2[(2a + (n - 1)d]
Where
a represents the first term of the sequence.
d represents the common difference.
n represents the number of terms in the sequence.
From the information given,
a = 10 seats
d = 2 seats (the seats in each row are increasing by 2)
n = 20(number of rows)
We want to determine the number of seats in 20 rows. Therefore
S20 = 20/2[(2×10 + (20 - 1)2]
S20 = 10(20 + 38) = 10×58
S = 580