Question

The sum of a G.P. with common ratio 3 is 364, and last term is 243, then the number of terms is.

• A. 6
• B. 5
• C. 4
• D. 10

Answer 1

Answer: (A)

6

Answer 2

$\frac { a r ^ { n } - a } { r - 1 } = 364$ $\Rightarrow \frac { a r ^ { n - 1 } \cdot r - a } { r - 1 } = 364$ …..(i)

⇒ $\frac { 3 \times 243 - a } { 2 } = 364$ $\Rightarrow a = 1$

Now, putting this in (i), n = 6.