MathematicsMedium89×since 2002Q5476Let 9=x1<x2<…<x79=x_{1} < x_{2} < \ldots < x_{7}9=x1<x2<…<x7 be in an A.P. with common difference d. If the standard deviation of x1,x2...,x7x_{1}, x_{2}..., x_{7}x1,x2...,x7 is 4 and the mean is xˉ\bar{x}xˉ, then xˉ+x6\bar{x}+x_{6}xˉ+x6 is equal to :A2(9+87)2\left(9+\frac{8}{\sqrt{7}}\right)2(9+78)B25C18(1+13)18\left(1+\frac{1}{\sqrt{3}}\right)18(1+31)D34Check answerSkip