The first term of a geometric sequence is 25, and the fourth term is 1\5.

Question

(a) Find the common ratio r.
r =

Find the fifth term.
a5 =

(b) Find the partial sum of the first eight terms.
S8 =

Answer 1

r^3 = (1/5)/25 = 1/125
so, r = 1/5

An = 5*(1/5)^(n-1) = 125/5^n

S8 = 25(1 - (1/5)^8)/(1 - 1/5) = 97656/3125