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)
Verified Correct Answer: B.
Step-by-Step Mathematical Solution
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)
Source: Myschool Past Questions Archive (Record #31473)