Question

(The first term of a G.P. is 4 and fourth term is 108. Find the common ratio and the sum of four
terms.)
[Ans. r =3; S4 = 160]

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Answer 1

First Term = a = 4

a4 = 108

ar^3 = 108

r^3 = 108/4

r^3 = 27

Common Ratio = r = 3.....●

Now,

Sum of 4 terms,

S4 = a(r^4 - 1) / (r-1)

= 4(3^4 - 1) / (3-1)

= 4(80)/2

S4 = 160......●

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Hope it was helpful.

Answer 2

n th term of a gp=(1st term)(r^n-1).

for complete answer,refer to the attached photo!!