Posted by jazzmin on Sunday, June 5, 2011 at 10:08pm.
. A person hired a firm to build a CB radio tower. The firm charges $100 for labor for
the first 10 feet. After that, the cost of the labor for each succeeding 10 feet is $25
more than the preceding 10 feet. That is, the next 10 feet will cost $125, the next
10 feet will cost $150, etc. How much will it cost to build a 90foot tower?

math  MathMate, Sunday, June 5, 2011 at 10:18pm
The cost is the arithmetic progression,
A(n)=A(1)+(n1)d
where A(1)=100, d=25
and the sum to the nth term is
S(n)=(n/2)(A(1)+A(n)
For n=9 (90')
S(n)=(9/2)(100 + 100+(91)*25)
=?