Question

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

Answer 1

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 <===

Answer 2

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