The, 8th sum of a gp is 640 if the first term is5 find the common ratio and 10th term solve

2 answers

5(r^8 - 1)/(r-1) = 640
Use that to find r, and then 5r^9

Not what I expected for r. Is there maybe a typo?
The 8th term of a g.p is 640, if the first term a is 5. Find (a)the common different r (b)the term term