math
posted by matt on .
The windows of a downtown office building are arranged so that each floor has six fewer windows than the floor below it. If the ground floor has 52 windows, how many total windows are on the first eight floors?

1St. = 52 Windows.
2nd = 52  6 = 46.
3rd = 46  6 = 40.
4th = 40  6 = 34.
5th = 34  6 = 28.
6th = 28  6 = 22.
7th = 22  6 = 16.
8th = 16  6 = 10.
Total = 52 + 46 + 40 + 34 + 28 + 22 + 16 + 10 = 248 Windows. 
What is the sum of a 12–term arithmetic sequence where the last term is 13 and the common difference is –10?