var randNum = Math.floor(Math.random()*5)+1;
document.getElementById("mastLeft").src = "http://grfx.cstv.com/schools/furm/graphics/furm-07-index-hdr-logo-" + randNum + ".jpg";
document.getElementById("mastRight").src = "http://grfx.cstv.com/schools/furm/graphics/furm-07-index-hrd-" + randNum + ".jpg";