Gujarati
8. Sequences and Series
easy

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

$10$

Solution

(a) $\frac{{a{r^n} – a}}{{r – 1}} = 364$

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

==> $\frac{{3 \times 243 – a}}{2} = 364$

$ \Rightarrow a = 1$

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

Standard 11
Mathematics

Similar Questions

Start a Free Trial Now

Confusing about what to choose? Our team will schedule a demo shortly.