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
Correct Answer: Option D
Explanation
ar = 8 …..(1)
ar^{3} = 32 …..(2)
divide (2) by (1)
r^{2} = 4 r = 2 ∴ a = 4
S =
a(r^{n} – 1)r – 1
S =
4(2^{4} – 1)2 – 1
= 60