Question:
If ratio of sum of first 6 terms of G.P. to sum of first 3 terms of G.P. is 9:1, what is the common ratio of G.P.?
Solve
In the question it is given that
S6/ S3 = 9/1
Therefore, we have to find the value of ‘r’.
{a(r6-1)/(r-1)} / {a(r3-1)/(r-1)} = 9/1
(r6-1) / (r3-1) = 9/1
(r3+1)(r6-1) / (r6-1) = 9/1
r3+1 = 9
r3 = 9-1
r3 = 8
r = 2
Check out more examples of Geometric Progression (G.P.), explained lucidly.