Body/girl probability

Answering the question: what is the percentage of boys in a society where couple only stop having babies when they have a boy.

by Alessandro Vernet

HTML

<script src="http://documentcloud.github.com/underscore/underscore.js"></script>
<div>Boys: <span id="boy-count"></span></div>
<div>Girls: <span id="girl-count"></span></div>
<div>Percentage of boys: <span id="boy-percentage"></span></div>

JavaScript

var FAMILIES = 100000;

var boyCount = 0;
var girlCount = 0;

_.each(_.range(FAMILIES), function() {
    while(true) {
        var isBoy = Math.random() < 0.5;
        if (isBoy) boyCount++; else girlCount++;
        if (isBoy) break;
    }
});

$("#boy-count").text(boyCount);
$("#girl-count").text(girlCount);
$("#boy-percentage").text(boyCount / (boyCount + girlCount) * 100);