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The sum of n terms of the G.P. 3, 6, 12, … is 381. Find the value of n. |
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Answer» Given: Sum of GP = 381 Where, a = 3, r = 6/3 = 2, n = ? By using the formula, Sum of GP for n terms = a(rn – 1 )/(r – 1) 381 = 3 (2n – 1)/ (2 - 1) 381 = 3 (2n – 1) 381/3 = 2n – 1 127 = 2n – 1 127 + 1 = 2n 128 = 2n 27 = 2n n = 7 ∴ value of n is 7 |
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