Find the sum of the first 18 terms of the progression 3, 6, 12……
-
A.
3(217 – 1) -
B.
3(218 – 1) -
C.
3(218 + 1) -
D.
3(217 – 1)
Correct Answer: Option B
Explanation
3 + 6 + 12 + …..18thy term
1st term = 3, common ratio (frac{6}{3}) = 2
n = 18, sum of GP is given by Sn = a(frac{(r^n – 1)}{r – 1})
s18 = 3(frac{(2^{18} – 1)}{2 – 1})
= 3(2^18 – 1)