(* simulate flipping a coin 100 times and record the outcome for each flip *)
outcomes = Table[RandomChoice[{0, 1}], {100}]

(* calculate the average outcome of the coin flips for each iteration *)
averages = Table[Mean[outcomes[[1;;i]]], {i, 1, 100}]

(* create a line plot of the average outcome over time *)
plot = ListLinePlot[averages, PlotRange -> {0, 1}, PlotLabel -> "Average outcome of coin flips over time", AxesLabel -> {"Iteration", "Average outcome"}, (* add a horizontal line at the expected value of 0.5 *) Epilog -> {Red, Dashed, Line[{{1, 0.5}, {100, 0.5}}]} ]

(* show the plot *)
plot 

With this description of what the code does:

This code adds a red dashed line to the plot, at the expected value of 0.5, to indicate the expected outcome of the coin flips. You can customize the line by changing its color, style, or position, or by adding additional lines to the plot.

I plugged it into Mathematica, and this is what I got: