Needs["Statistics`DescriptiveStatistics`"]

Needs["Statistics`DataManipulation`"]

Needs["Statistics`HypothesisTests`"]

Needs["Statistics`ContinuousDistributions`"]

Weight={
	{1 , 23.1000004 },{2 , 21.2999992 },{3 , 22 },{4 , 21.3999996 },{5 , 21.7999992 },{6 , 20.6000004 },{7 , 20.1000004 },{8 , 21.3999996 },{9 , 21.5 },{10 , 20.2000008 },{11 , 20.2999992 },{12 , 20.1000004 },{13 , 21.7000008 },{14 , 21 },{15 , 21.6000004 },{16 , 21.3999996 },{17 , 20.3999996 },{18 , 22.7999992 },{19 , 21.1000004 },{20 , 20.7000008 },{21 , 21.6000004 },{22 , 22.3999996 },{23 , 21.2999992 },{24 , 21.1000004 },{25 , 20.1000004 },{26 , 21.2000008 },{27 , 19.8999996 },{28 , 21.1000004 },{29 , 21.6000004 },{30 , 21.2999992 },
		{31 , 24.2999992 }
		};

\(MeanTest[Column[Weight, 2], 23\ , 

      \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 
      KnownVariance\  -> \ Variance[Column[Weight, 2]], \ 

      \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ TwoSided -> True, \ 

      \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ SignificanceLevel -> 0.01, 

      \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ FullReport\  -> \ True]\)

Weight2 = 
      Table[{Weight[[a]][[2]],  Random[]}, {a, 1, 31}];

TWeight = Select[Weight2, #[[2]] > 0.75&]

\(MeanTest[Column[TWeight, 1], 23\ , 

      \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ TwoSided -> True, \ 

      \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ SignificanceLevel -> 0.01, 

      \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ FullReport\  -> \ True]\)