Question

Find the number of terms in the GP : 6, 12, 24, ...., 1536

• A. 7
• B. 11
• C. 9
• D. 8

Answer 1

Answer:

C. 9

$a=6, r=12/6=2, a_n=1536$

$a_n=ar^{n-1}$

$1536=6\times2^{(n-1)}$

$2^{(n-1)}=1536/6=256$

$2^{(n-1)}=2^8$

$n-1=8$

$n=9$