1. a square has a side of 2 decimeters. a new square is formed by joining the midpoints of the sides. If this procedure is reoeated 6 times, what is the perimetet and area of the seventh square
2. find the sum of those numbers between 15 and 810 which have 8 as their units digit
3. in an arithmetic sequence, the sixth term is twice the 3rd term and the 30th term is 60. find the common difference?