function change_div_bg(div_id) {
    var div = document.getElementById(div_id);
    div.style.backgroundImage = "url('img/small_logo_"+Math.floor(Math.random()*6)+".jpg')";

//  function random_didunow(div_id) {
//    var div = document.getElementById(div_id);
    var div = document.getElementById('info');
    var duk = Array();
    duk[0] = '<strong>Did you know?</strong><br />A0 measures 841x1189mm and has an area of one square metre<br /><a href="paper_sizes.html">more >></a>';
    duk[1] = '<strong>Did you know?</strong><br />The aspect ratio of all ISO paper is the square root of 2 – too clever by half!<br /><a href="paper_sizes.html">more >></a>';
    duk[2] = '<strong>Did you know?</strong><br />It has been estimated that humans can distinguish roughly 10 million different colours.<br /><a href="color.html">more >></a>';
    duk[3] = '<strong>Did you know?</strong><br />Colour can help increase brand recognition by up to 80%.<br /><a href="color.html">more >></a>';
    duk[4] = '<strong>Did you know?</strong><br />It is physically impossible to fold a piece of paper in half more than 8 times.<br /><a href="folding_sizes.html">more >></a>';
    duk[5] = '<strong>Did you know?</strong><br />There are 16 different ways to fold a piece of paper.<br /><a href="folding_sizes.html">more >></a>';
    div.innerHTML = duk[Math.floor(Math.random()*6)];
//  }
  

}