Q13 of 176 Page 20

The fifth term of a G.P. is 81 whereas its second term is 24. Find the series and sum of its first eight terms.

Nth term of GP is Tn = arn - 1


T5 = a.r4


81 = a.r4…(1)


Nth term of GP is Tn = arn - 1


T2 = a.r1


24 = a.r1…(2)


Divide 1 by 2


⇒


⇒


⇒


Substituting r in 2 we get,


a = 16


∴ The series is 16, 24, 54, …


∴ Sum of GP for n terms = …(1)


⇒ a = 16, r = , n = 8


∴ Substituting the above values in (1) we get,


⇒


⇒


⇒ 788.125


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