An auditorium has 20 rows with 10 seats in the first row, 12 in the second row, 14 in the third row, and so forth. how many seats are in the auditorium?

there are 580 seats

Step-by-step 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

  (A) -5   and   (C) -3

Step-by-step explanation:

See attached graph.  They intersect when x = -5 and when x = 3