The sum of n terms of the G.P. 3, 6, 12, … is 381. Find the value of n.

Given:


Sum of GP = 381


∴ Common Ratio = r =


a = 3


To find: Number of terms = n.


Sum of GP for n terms =


⇒


⇒ 127 = 2n - 1


⇒ 128 = 2n


⇒ 27 = 2n


∴ n = 7.


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