Solution(By Examveda Team)
$$\eqalign{
& \frac{x}{{\left( {2x + y + z} \right)}} = a \cr
& \Rightarrow x = a\left( {2x + y + z} \right)\,....(1) \cr
& \frac{y}{{\left( {x + 2y + z} \right)}} = a \cr
& \Rightarrow y = a\left( {x + 2y + z} \right)\,....(2) \cr
& \frac{z}{{\left( {x + y + 2z} \right)}} = a \cr
& \Rightarrow z = a\left( {x + y + 2z} \right)\,....(3) \cr
& {\text{Adding (1), (2) and (3) we get:}} \cr
& x + y + z \cr
& = a\left( {4x + 4y + 4z} \right) \cr
& \Rightarrow a = \frac{{\left( {x + y + z} \right)}}{{4\left( {x + y + z} \right)}} \cr
& \Rightarrow a = \frac{1}{4} \cr} $$
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