Question

Find the indicated sum for the arithmetic series:

Answer 1

\[\sum_{k=1}^{15} (50-20k)\]

Answer 2

well find the 1st and last terms

k = 1 1st term = 30 k = 15 last term = -250

the the sum can be found by

\[S_{n} = \frac{n}{2}[ a + l]\]

n = number of term, 15 in your question, a = 1st term, l = last term

just substitute and then evaluate.

Answer 3

so you plug in 15 for n?

Answer 4

yes..

Answer 5

alright so the answer is -1650?

Answer 6

yep, thats looks like the right answer.

Answer 7

okay thank you!:)