The ratio of the forth and 12th terms of a g.p. with positive common ratio is 1:256. If the difference of two terms be 61.2. Find the sum of 8 term of this series.

Answer 1

ar^3/ar^11 = 1/256
1/r^8 = 1/256
r = 2

Now you can find a, so the sum

S8 = a(2^8-1)/(2-1) = 127a

Answer 2

a=0.03