Question

Compute the sum of the first $6$ terms of the GP $3,6,12,\mathrm{24...}$

• A. $189$
• B. $289$
• C. $389$
• D. $489$

Answer 1

The correct option is A $189$

Given geometric progression is $3,6,12,24,....$

Here first term $=a=3$, common ratio $r=2$ and $n-6$

We have $S_n=\frac{a(1-r^n)}{1-r}$

$=\frac{3(1-2^6)}{1-2}$

$=3\left(63\right)$

$=189$