Imagine a room full of 100 people with 100 dollars each. With every tick of the clock, every person with money gives a dollar to one randomly chosen other person. After some time progresses, how will the money be distributed?

wilensky.js

// paste me into console to explore the counterintuitive problem found here:
// http://www.decisionsciencenews.com/2017/06/19/counterintuitive-problem-everyone-room-keeps-giving-dollars-random-others-youll-never-guess-happens-next/

// setup: tweak as needed
var rounds = 10, turns = 1000, max = 100, start = 100; 

// play one round
var round = function () {
  
  // setup
  var a = [];
  
  // everybody gets the same number of things to start
  for (var i = 0; i < max; i = i + 1) {
    a.push(start);
  }

  // everybody who has at least one thing: give one to somebody else
  var turn = function () {
    for (var i = 0; i < max; i = i + 1) {
      if (a[i]) {
        a[i] = a[i] - 1;
        var r = Math.floor(Math.random() * max);
        a[r]++;
      }
    }
  };
  
  // run some turns
  for (var t = 0; t < turns; t = t + 1) {
    turn();
  }
  
  // sort so it's easy to spot highs and lows
  a.sort(function (a, b) { 
    return  b - a;
  });

  //return results
  return a;
};

// play some rounds and log them to console
for (var i = 0; i < rounds; i = i + 1) {
  console.log(round());
}

Nice. I copied this into a JSFiddle so people could play with it without opening a console.
https://jsfiddle.net/jones1618/n5w5nyo6/