Question

The first term of a G.P. is 7, the last term is 448 and sum of all terms is 889, then the common ratio is.

• A. 5
• B. 4
• C. 3
• D. 2

Answer 1

Answer: (D)

2

Answer 2

$a = 7$ and $a r ^ { n - 1 } = 448$

Now,$S _ { n } = \frac { a \left( r ^ { n } - 1 \right) } { r - 1 } = 889$ $\Rightarrow \frac { \left( a r ^ { n - 1 } \cdot r - a \right) } { r - 1 } = 889$

⇒ $\frac { 448 r - 7 } { r - 1 } = 889$ ⇒ $r = 2$.