If a_1, a_2, a_3, .... a_{21} are in A.P. and | vedclass

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Question

Let $\,\,a_{3}+a_{19}=a_{5}+a_{17}=2 a_{11}=k$

given $\,\,a_{3}+a_{5}+a_{11}+a_{17}+a_{19}=10$

$\Rightarrow \frac{5}{2} \mathrm{k}=10 \Rightarro

Vedclass · Accepted Answer

$42$

Vedclass · Answer

Let $\,\,a_{3}+a_{19}=a_{5}+a_{17}=2 a_{11}=k$

given $\,\,a_{3}+a_{5}+a_{11}+a_{17}+a_{19}=10$

$\Rightarrow \frac{5}{2} \mathrm{k}=10 \Rightarrow \mathrm{k}=4$

$	ext { so } a_{1}+a_{21}=4$        ....$(1)$

$\sum\limits_{r = 1}^{21} {{a_r} = \frac{{21}}{2}\left[ {{{m{a}}_1} + {{m{a}}_{21}}} ight] = 42} $

If $a_1, a_2, a_3, .... a_{21}$ are in $A.P.$ and $a_3 + a_5 + a_{11}+a_{17} + a_{19} = 10$ then the value of $\sum\limits_{r = 1}^{21} {{a_r}} $ is

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