First slide

Geometric progression

Question

The ratio of sum of first three terms of a G.P to the sum of first six terms is 64:91 , the common ratio of G.P. is

Moderate

A

$\frac{1}{4}$
B

$\frac{3}{4}$
C

$\frac{5}{4}$
D

$\frac{7}{4}$

Solution

$Given \frac{S_{3}}{S_{6}} = \frac{64}{91} = \frac{a (r^{3} - 1)}{a (r^{6} - 1)}$
$\Rightarrow \frac{(r^{3} - 1)}{(r^{3} + 1) (r^{3} - 1)} = \frac{64}{91} \Rightarrow r^{3} = \frac{27}{64} ∴ r = \frac{3}{4}$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App