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How many terms of G.P. `3,3^2,3^3,dotdotdot`are needed to give the sum 120? |
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Answer» In the given GP, `a = 3, r = 3` `S_n = 120` `:. a(r^n-1)/(r-1) = 120` `=>3(r^n-1)/(3-1) = 120` `=>3^n -1 = 80 => 3^n = 81` `=> 3^n = 3^4` `n = 4` |
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