If five G.M.’s are inserted between 486 and 2/3 then fourth G.M. will be

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Gujarati

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8. Sequences and Series

easy

If five $G.M.’s$ are inserted between $486$ and $2/3$ then fourth $G.M.$ will be

A

$4$

B

$6$

C

$12$

D

$-6$

Solution

(b) Let ${G_1},{G_2},{G_3},{G_4},{G_5}$ be the $G.M.’s$ are inserted between $486$ and $2/3$.

So total terms are $7$.

${T_n} = a{r^{n – 1}}$

==> $2/3 = 486$${(r)^6}$

$ \Rightarrow r = 1/3$

Hence $4^{th}$ $G.M.$ will be,

${T_5} = a{r^4} = 486\,{(1/3)^4} = 6$.

Standard 11

Mathematics

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