Posted by Anna on Sunday, May 8, 2011 at 7:54pm.
We're working on geometric and athrimetic series and I really don't know where to start with this except that t sub 1 = 101
How would I find the sum of the multiples of 5 between 101 and 2001 help

AlgebraPlease help  Damon, Sunday, May 8, 2011 at 8:14pm
well, the first multiple of 5 in that interval is 105.
The last is 2000.
105 + 110 + 115 + ........ 2000
n1 = (2000105)/5 = 379
n = 380
Sum = (n/2)(a1+an) = (380/2)(2105)
=399,950 
AlgebraPlease help  Anna, Sunday, May 8, 2011 at 8:19pm
Thank you very much

AlgebraPlease help  Damon, Sunday, May 8, 2011 at 8:21pm
You are welcome :)