Mathematics

If the second and fourth term of a G.P are 8 and 32 respectively,what is…

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)

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