Calculate S_24 for the arithmetic sequence in which a_13=1.9 and the common difference is d=3.7

a.-42.5

b. 42.6

c.-59.4

d. 1.2

An=a1+d (n-1)

a13=1.9

1.9=a1+3.7 (13-1)

1.9=a1+3.7 (12)

1.9=a1+44.4

minus 44.4 both sides

-42.5=a1

an=-42.5+3.7 (n-1)

S_24, so sum all theway up to a24

S_n = (n (a1+an)) / 2

a1=-42.5

a24=-42.5+3.7 (24-1) = 42.6

S_n = (24 (-42.5+42.6)) / 2

S_n = (24 (0.1)) / 2

S_n = (2.4) / 2

S_n=1.2

D