Question

What is the sum of a 30–term arithmetic sequence where the first term is 74 and the last term is –100?

a.–468
b.–442
c. –416
d. –390

Answer 1

the general formula is:\[\frac{n(first+last)}{2}\]

Answer 2

n(74-100)/2
-26n/2
do i go further & simply ?

Answer 3

so far so good; but yes go further. n=30 in this case

some other ideas i have are

30/2 = 15

74-100 = 26

since the last digit of 6*5 = 30 is zero; it should end in a 0

Answer 4

so it's -390

Answer 5

i didnt do any thorough mathing, but all signs point to yes :)

Answer 6

Thanks for the help