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?

248 


windows on first floor = 52 

windows on 8th floor (52 - 6 * 7) = 10 

average windows = (52 + 10)/2 = 62/2 = 31 

8 floors * 31 average windows = 248.