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DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
   Dynamic[Legended[PieChart[Thread[Style[#[[All, 2]], #[[All, 1]] /.
        {True -> Red, False -> Green}] ], 
      ChartStyle -> {Green, Red}] &@ 
      Tally@Sort@RandomChoice[{True, False}, n], 
     SwatchLegend[{Green, Red}, {False, True}]]]}]]

Alternatively (thanks: Brett Champion):

DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
   Dynamic[PieChart[Thread[Style[#[[All, 2]], #[[All, 1]] /. 
                      {True -> Red, False -> Green}]], 
       ChartLegends -> SwatchLegend[{Green, Red}, {False, True}]] &@
     Tally@Sort@RandomChoice[{True, False}, n]]}]]

DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
   Dynamic[Legended[PieChart[Thread[Style[#[[All, 2]], #[[All, 1]] /.
        {True -> Red, False -> Green}] ], 
      ChartStyle -> {Green, Red}] &@ 
      Tally@RandomChoice[{True, False}, n], 
     SwatchLegend[{Green, Red}, {False, True}]]]}]]

Alternatively (thanks: Brett Champion):

DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
   Dynamic[PieChart[Thread[Style[#[[All, 2]], #[[All, 1]] /. 
                      {True -> Red, False -> Green}]], 
       ChartLegends -> SwatchLegend[{Green, Red}, {False, True}]] &@
     Tally@RandomChoice[{True, False}, n]]}]]

DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
   Dynamic[Legended[PieChart[#[[All, 2]], ChartStyle -> {Green, Red}] &@
                    Tally@Sort@RandomChoice[{True, False}, n], 
           SwatchLegend[{Green, Red}, {False, True}]]]}]]

Alternatively (thanks: Brett Champion):

DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
         Dynamic[PieChart[#[[All, 2]], ChartStyle -> {Green, Red}, 
                           ChartLegends -> SwatchLegend[{Green, Red}, {False, True}]] &@
                 Tally@Sort@RandomChoice[{True, False}, n]]}]]

DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
   Dynamic[Legended[PieChart[Thread[Style[#[[All, 2]], #[[All, 1]] /.
        {True -> Red, False -> Green}] ],  
      ChartStyle -> {Green, Red}] &@  
      Tally@Sort@RandomChoice[{True, False}, n], 
     SwatchLegend[{Green, Red}, {False, True}]]]}]]

Alternatively (thanks: Brett Champion):

DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
   Dynamic[PieChart[Thread[Style[#[[All, 2]], #[[All, 1]] /.  
                      {True -> Red, False -> Green}]],  
       ChartLegends -> SwatchLegend[{Green, Red}, {False, True}]] &@
     Tally@Sort@RandomChoice[{True, False}, n]]}]]

DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
   Dynamic[Legended[PieChart[#[[All, 2]], ChartStyle -> {Green, Red}] &@
                    Tally@Sort@RandomChoice[{True, False}, n], 
           SwatchLegend[{Green, Red}, {False, True}]]]}]]

DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
   Dynamic[Legended[PieChart[#[[All, 2]], ChartStyle -> {Green, Red}] &@
                    Tally@Sort@RandomChoice[{True, False}, n], 
           SwatchLegend[{Green, Red}, {False, True}]]]}]]

Alternatively (thanks: Brett Champion):

DynamicModule[{n = 20}, 
 Column[{Row[{Slider[Dynamic[n], {1, 100, 1}], Dynamic[n]}], 
         Dynamic[PieChart[#[[All, 2]], ChartStyle -> {Green, Red}, 
                          ChartLegends -> SwatchLegend[{Green, Red}, {False, True}]] &@
                 Tally@Sort@RandomChoice[{True, False}, n]]}]]