Question

Which term of the GP 1,2,4,8,.... is 512 ?

• A. 8
• B. 9
• C. 10
• D. 11

Answer 1

The correct option is C 10

$a=1,r=2$
$an=a{r}^{n-1}=512$
$1\left(2^{n-1}\right)=512$
$2^{n-1}=512=2^9$
$n-1=9$
$n=10$