Question

What is the sum of a 22-term arithmetic sequence where the first term is 55 and the last term is -29?
Choose one answer.
a. 260
b. 286
c. 312
d. 338

Answer 1

\(\Large \color{Black}{\Rightarrow {n \over 2}({a_1 + a_n}) }\)
This is the formula. Let's substitute right there.

\(\Large \color{Black}{\Rightarrow {22 \over 2}(55 + -29) }\)

\(\Large \color{Black}{\Rightarrow 11(55 - 29) }\)

\(\Large \color{Black}{\Rightarrow 11(26) }\)

\(\Large \color{Black}{\Rightarrow 286 }\)

Answer 2

use sum formula

Sn = [n(a1 + an)]/2

Answer 3

K thanks!