If the second and fourth term of a G.P are 8 and 32 respectively,what is the sum of the first four terms?
A
28
B
40
C
48
D
60
E
68
Verified Correct Answer: D.
Step-by-Step Mathematical Solution
ar = 8 .....(1)
ar3 = 32 .....(2)
divide (2) by (1)
r2 = 4 r = 2 ∴ a = 4
S = a(rn - 1)/r - 1
S = 4(24 - 1)/2 - 1 = 60
Source: Myschool Past Questions Archive (Record #22342)