Plot of histogram similar to output from @risk

Try this:

With[{dist = CDF[mydist]},
 Manipulate[
  Histogram[mydata, Automatic, "Probability",
   PlotRange -> {MinMax@mydata, All},
   PlotLabel -> 
    StringForm["Percent Inside: ``" , 
     dist[bounds[[2]]] - dist[bounds[[1]]]],
   Epilog ->
    {
     EdgeForm[None],
     GrayLevel[1, .5],
     Rectangle[
      {Min@mydata, 0},
      {bounds[[1]], 1000000}
      ],
     Rectangle[
      {bounds[[2]], 0},
      {Max@mydata, 1000000}
      ]
     }
   ],
  {
   {bounds, Rescale[{.25, .75}, {0, 1}, MinMax@mydata]},
   Sequence @@ MinMax@mydata,
   ControlType -> IntervalSlider
   }
  ]
 ]

A starting point:

BlockRandom[SeedRandom[42]; (* for reproducibility *)
            mydata = RandomVariate[TriangularDistribution[{100, 400}, 200], 5000]];

DynamicModule[{hd, hist, xmin, xmax, yr},
              Manipulate[Show[hist, 
                              Plot[PDF[hd, x], {x, h[[1, 1]], h[[2, 1]]},
                                   Exclusions -> None, Filling -> {1 -> Axis},
                                   FillingStyle -> Opacity[0.8, Pink],
                                   PlotPoints -> 95, PlotRange -> yr, 
                                   PlotStyle -> Directive[AbsoluteThickness[2], Pink]],
                              Axes -> None, Frame -> True,
                              GridLines -> {{h[[1, 1]], h[[2, 1]]}, None}, 
                              Method -> {"GridLinesInFront" -> True}, 
                              PlotLabel -> StringForm["``%",
                                                      100 Round[Abs[CDF[hd, h[[2, 1]]] -
                                                                    CDF[hd, h[[1, 1]]]],
                                                                0.001]]],
                         {{h, {{xmin, 0}, {xmax, 0}}}, Locator, Appearance -> None},
                         Initialization :> (hd = HistogramDistribution[mydata];
                                            {xmin, xmax} = First[hd["Domain"]]; 
                                            hist = Histogram[mydata, Automatic, "PDF", 
                                            ChartBaseStyle ->
                                            Directive[EdgeForm[], LightPink]];
                                            yr = Last[Charting`get2DPlotRange[hist]];)]]