An auditorium has 30 rows of seats. The first row has 20 seats, the second row has 22 seats, the third row has 24 seats, and so on. What is the total seating capacity of the auditorium

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

52

54

56

58

60

62

64

66

68

70

72

74

76

78

80

Equals

1438

An = a1 + (n-1) * d

n = term to find = 30

a1 = first term = 20

d = common difference = 2

a30 = 20 + (30 - 1) * 2

a30 = 20 + 29 * 2

a30 = 20 + 58

a30 = 78

sn = (n (a1 + a30)) / 2

s30 = (30 (20 + 78) / 2

s30 = (30 (98) / 2

s30 = 2940/2

s30 = 1470 <===