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The first, third and eighth terms of an A.P with common difference 9 (taken in that order) are in G.P. The seventh term of A.P is

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answer is B.

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Detailed Solution

$a, a + 9, a + 18, \dots now a_{1}, a_{3} and a_{8} are in G.P.$

$\begin{array}{l} i.e. a, a+18anda+63 are in G.P. \\ (a + 18)^{2} = a (a + 63) \\ \to a = 12, d = 9 \\ ∴ a_{7} = a + 6 d = 12 + 54 = 66 \end{array}$

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