Answer:
950
Step-by-step explanation:
The common difference is 4, so the general term can be written:
... an = 14 + 4(n -1)
The value of n for the last term is ...
... 86 = 14 + 4(n -1) . . . . . the computation for the last term, 86
... 72 = 4(n -1) . . . . . . . . . subtract 14
... 18 = n -1 . . . . . . . . . . . divide by 4
... 19 = n . . . . . . . . . . . . . add 1
Your series has 19 terms. The first term is 14 and the last is 86, so the average term is (14+86)/2 = 50. Since there are 19 terms, the sum of them is ...
... 19×50 = 950
