Question

What is the sum of the series?​

Answer 1

- 10

Explanation:

Substitute k = 3, 4, 5, 6 into the expression and sum the terms, that is

-5(3) + 20 - 5(4) + 20 - 5(5) + 20 - 5(6) + 20

= - 15 + 20 - 20 + 20 - 25 + 20 - 30 + 20

= 5 + 0 - 5 - 10

= - 10