Question

Find the sum of the first 40 terms of an arithmetic series whose first term is 7 and 40th term is 115. Type answer as an integer (no decimals)

arithmetic sum formula:
Sn = (a1 +
+ an)
geometric sum formula:
az (1 - p)
S =
1-r
Answer:

Answer 1

2440

Explanation:

an=115

a=7

Sn=n/2(a+an) [Where n is no. of terms]

= 40/2(7+115)

= 20(122)

= 2440