What is the sum if the first 22 terms of the following series? 86 + 79 + 72 + 65 + 58 + ...

Seems to be an arythmetic sequence

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

where

Sn means sum of all terms up the nth term

n=number of terms

a1=first term

an=nth term

so from 86 to the 22th term is from a1 to a22

find teh sequence

miknus 7 each time

an=a1+d (n-1)

an=87-7 (n-1)

find 22n term

a22=87-7 (22-1)

a22=87-7 (21)

a22=87-147

a22=-60

S22=[22 (87-60) ]/2

S22=[22 (27) ]/2

S22=594/2

S22=297

the sum is 297