Question

A geometric sequence is a sequence of numbers where the next term equals to

the previous term multiplied by a common factor (for example, (3, 6, 12, 24, ...)

is a geometric sequence with the first term ”3” and the common factor ”2”). If

the 5th term of a geometric sequence is 24 and the 7th term is 144, what is the

first term of the sequence?

(A) 2

(B) 3/2

(C) 2/3

(D) 1/3

(E) 1/4

Answer 1

C

Explanation:

Let the first term be a and the common ratio be r.

ATQ, ar^4=24 and ar^6=144, r=sqrt(6) and a=24/(sqrt(6))^2=24/36=2/3